#include<bits/allocator.h>
#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("avx2,fma,bmi,bmi2,popcnt,lzcnt,tune=native")
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define int128 __int128_t
#define double long double
#define gcd __gcd
#define lcm(a, b) ((a)/gcd(a, b)*(b))
#define sqrt sqrtl
#define log2 log2l
#define log10 log10l
#define floor floorl
#define yes cout << "YES"
#define no cout << "NO"
#define trav(i, a) for (auto &i: (a))
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define sz(a) (int)a.size()
#define Max(a) *max_element(all(a))
#define Min(a) *min_element(all(a))
#define Find(a, n) (find(all(a), n) - a.begin())
#define Count(a, n) count(all(a), n)
#define Upper(a, n) (upper_bound(all(a), n) - a.begin())
#define Lower(a, n) (lower_bound(all(a), n) - a.begin())
#define next_perm(a) next_permutation(all(a))
#define prev_perm(a) prev_permutation(all(a))
#define sorted(a) is_sorted(all(a))
#define sum(a) accumulate(all(a), 0)
#define sumll(a) accumulate(all(a), 0ll)
#define Sort(a) sort(all(a))
#define Reverse(a) reverse(all(a))
#define Unique(a) Sort(a), (a).resize(unique(all(a)) - a.begin())
#define pb push_back
#define eb emplace_back
#define popcount __builtin_popcount
#define popcountll __builtin_popcountll
#define clz __builtin_clz
#define clzll __builtin_clzll
#define ctz __builtin_ctz
#define ctzll __builtin_ctzll
#define open(s) freopen(s, "r", stdin)
#define write(s) freopen(s, "w", stdout)
#define fileopen(s) open((string(s) + ".inp").c_str()), write((string(s) + ".out").c_str());
#define For(i, a, b) for (auto i = (a); i < (b); ++i)
#define Fore(i, a, b) for (auto i = (a); i >= (b); --i)
#define FOR(i, a, b) for (auto i = (a); i <= (b); ++i)
#define ret(s) return void(cout << s);
constexpr int mod = 1e9 + 7, mod2 = 998244353;
constexpr double eps = 1e-9;
const double PI = acos(-1);
constexpr ull npos = string::npos;
constexpr int dx[] = {1, 0, -1, 0, 1, 1, -1, -1}, dy[] = {0, 1, 0, -1, 1, -1, 1, -1};
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using cd = complex<double>;
mt19937 mt(chrono::system_clock::now().time_since_epoch().count());
mt19937_64 mt64(chrono::system_clock::now().time_since_epoch().count());
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<double> vdo;
typedef vector<vdo> vvdo;
typedef vector<string> vs;
typedef vector<pii> vpair;
typedef vector<vpair> vvpair;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<char> vc;
typedef vector<vc> vvc;
typedef vector<cd> vcd;
typedef priority_queue<int> pq;
typedef priority_queue<int, vi, greater<int>> pqg;
typedef priority_queue<ll> pqll;
typedef priority_queue<ll, vll, greater<ll>> pqgll;
ll add(ll a, ll b, int m) {a = (a >= m ? a % m: a);b = (b >= m ? b % m: b);a+=b;return a >= m ? a - m: a;}
ll sub(ll a, ll b, int m) {a = (a >= m ? a % m: a);b = (b >= m ? b % m: b);a-=b;return a < 0 ? a + m: a;}
ll mul(ll a, ll b, int m) {a = (a >= m ? a % m: a);b = (b >= m ? b % m: b);return a*b % m;}
ll bin_mul(ll a, ll b, ll m) {a = (a >= m ? a % m: a);b = (b >= m ? b % m: b);ll x = 0;while (b) {if (b & 1) x = (x + a) % m;a = (a + a) % m;b>>=1;}return x;}
ll bin_pow(ll a, ll b, ll m) {ll x = 1;a = (a >= m ? a % m: a); while (b) {if (b & 1) x = bin_mul(x, a, m);a = bin_mul(a, a, m);b>>=1;}return x;}
ll power(ll a, ll b, int m) {ll x = 1;a = (a >= m ? a % m: a); while (b) {if (b & 1) x = x*a % m;a = a*a % m;b>>=1;}return x;}
ll power(ll a, ll b) {ll x = 1;while (b) {if (b & 1) x = x*a;a = a*a;b>>=1;}return x;}
ll ceil(ll a, ll b) {return (a + b - 1)/b;}
ll to_int(const string &s) {ll x = 0; for (int i = (s[0] == '-'); i < sz(s); ++i) x = x*10 + s[i] - '0';return x*(s[0] == '-' ? -1: 1);}
bool is_prime(ll n) {if (n < 2) return 0;if (n < 4) return 1;if (n % 2 == 0 || n % 3 == 0) return 0;for (ll i = 5; i*i <= n; i+=6) {if(n % i == 0 || n % (i + 2) == 0) return 0;}return 1;}
bool is_square(ll n) {ll k = sqrt(n); return k*k == n;}
ll factorial(int n) {ll x = 1;for (int i = 2; i <= n; ++i) x*=i;return x;}
ll factorial(int n, int m) {ll x = 1;for (ll i = 2; i <= n; ++i) x = x*i % m;return x;}
bool is_power(ll n, ll k) {while (n % k == 0) n/=k;return n == 1ll;}
string str(ll n) {if (n == 0) return "0"; string s = ""; bool c = 0; if (n < 0) c = 1, n = -n; while (n) {s+=n % 10 + '0'; n/=10;} if (c) s+='-'; Reverse(s); return s;}
string repeat(const string &s, int n) {if (n < 0) return ""; string x = ""; while (n--) x+=s; return x;}
string bin(ll n) {string s = ""; while (n) {s+=(n & 1) + '0'; n>>=1;} Reverse(s); return s;}
void sieve(vector<bool> &a) {int n = a.size(); a[0] = a[1] = 0; for (int i = 4; i < n; i+=2) a[i] = 0; for (int i = 3; i*i < n; i+=2) {if (a[i]) {for (int j = i*i; j < n; j+=(i << 1)) a[j] = 0;}}}
void sieve(bool a[], int n) {a[0] = a[1] = 0; for (int i = 4; i < n; i+=2) a[i] = 0; for (int i = 3; i*i < n; i+=2) {if (a[i]) {for (int j = i*i; j < n; j+=(i << 1)) a[j] = 0;}}}
void sieve(vector<int> &a) {int n = a.size(); for (int i = 2; i < n; i+=2) a[i] = 2; for (int i = 3; i*i < n; i+=2) {if (!a[i]) {for (int j = i; j < n; j+=(i << 1)) a[j] = i;}} for (int i = 3; i < n; i+=2) {if (!a[i]) a[i] = i;}}
void sieve(int a[], int n) {for (int i = 2; i < n; i+=2) a[i] = 2; for (int i = 3; i*i < n; i+=2) {if (!a[i]) {for (int j = i; j < n; j+=(i << 1)) a[j] = i;}} for (int i = 3; i < n; i+=2) {if (!a[i]) a[i] = i;}}
vector<pii> factorize(int n) {vector<pii> a; for (int i = 2; i*i <= n; ++i) {if (n % i == 0) {int k = 0; while (n % i == 0) ++k, n/=i; a.emplace_back(i, k);}} if (n > 1) a.emplace_back(n, 1); return a;}
int rand(int l, int r) {return uniform_int_distribution<int>(l, r)(mt);}
ll rand(ll l, ll r) {return uniform_int_distribution<ll>(l, r)(mt64);}
int Log2(int n) {return 31 - __builtin_clz(n);}
ll Log2(ll n) {return 63 - __builtin_clzll(n);}
template<class T> void compress(vector<T> &a) {vector<T> b; for (T &i: a) b.push_back(i); sort(all(b)); b.resize(unique(all(b)) - b.begin()); for (T &i: a) i = lower_bound(all(b), i) - b.begin() + 1;}
template<class A, class B> bool ckmin(A &a, const B &b) {return a > b ? a = b, 1: 0;}
template<class A, class B> bool ckmax(A &a, const B &b) {return a < b ? a = b, 1: 0;}
template<class A, class B> istream& operator>>(istream& in, pair<A, B> &p) {in >> p.first >> p.second; return in;}
template<class A, class B> ostream& operator<<(ostream& out, const pair<A, B> &p) {out << p.first << ' ' << p.second; return out;}
template<class T> istream& operator>>(istream& in, vector<T> &a) {for (auto &i: a) in >> i; return in;}
template<class T> ostream& operator<<(ostream& out, const vector<T> &a) {for (auto &i: a) out << i << ' '; return out;}
template<class T> istream& operator>>(istream& in, vector<vector<T>> &a) {for (auto &i: a) in >> i; return in;}
template<class T> ostream& operator<<(ostream& out, const vector<vector<T>> &a) {for (auto &i: a) out << i << '\n'; return out;}
template<class T> istream& operator>>(istream& in, deque<T> &a) {for (auto &i: a) in >> i; return in;}
template<class T> ostream& operator<<(ostream& out, const deque<T> &a) {for (auto &i: a) out << i << ' '; return out;}
// istream& operator>>(istream& in, __int128_t &a) {string s; in >> s; a = 0; for (int i = (s[0] == '-'); i < sz(s); ++i) a = a*10 + s[i] - '0'; a*=(s[0] == '-' ? -1: 1); return in;}
// ostream& operator<<(ostream& out, __int128_t a) {string s = ""; if (a < 0) out << '-', a = -a; if (a == 0) s+='0'; while (a > 0) {s+=(int)(a % 10) + '0'; a/=10;} Reverse(s); out << s; return out;}
template < auto P_ > class MontgomeryModInt
{
using S = decltype(P_); static_assert(is_same_v < S, int > || is_same_v < S, long long >);
static_assert(P_ & 1 && 0 < P_ && P_ < ( (S)1 << ( sizeof(S) * 8 - 2 ) ));
using U = conditional_t < is_same_v < S, int >, unsigned, unsigned long long >; using D = conditional_t < is_same_v < S, int >, unsigned long long, __uint128_t >;
inline constexpr static U uinv(U x) { U y = x; for ( int i = is_same_v < S, int > ? 4 : 5 ; i-- ; ) y *= 2 - x * y; return y; }
constexpr static U P = P_, P2 = P << 1, R = -uinv(P), R2 = -(D)P % P; static_assert(P * R == -1);
inline constexpr static U reduce(D x) { return ( x + (U)x * R * (D)P ) >> ( sizeof(U) * 8 ); }
inline constexpr MontgomeryModInt(U x, int) : v(x) {} U v;
public:
inline constexpr static S mod() { return P; }
inline constexpr MontgomeryModInt() : v(0) {}
inline constexpr MontgomeryModInt(const MontgomeryModInt &x) : v(x.v) {}
template < class T, enable_if_t < numeric_limits < T >::is_integer, int > = 0 > inline constexpr MontgomeryModInt(T x) : v(reduce((D)R2 * ( numeric_limits < T >::is_signed && x < 0 ? ( ( x + P < 0 ) && ( x %= P ), x + P ) : ( ( sizeof(T) > sizeof(U) && x >= (T)1 << sizeof(U) ) && ( x %= P ), x ) ))) {}
inline constexpr S val()const { U x = reduce(v); return ( x - P ) >> ( sizeof(U) * 8 - 1 ) ? x : x - P; }
template < class T, enable_if_t < numeric_limits < T >::is_integer, int > = 0 > explicit inline constexpr operator T()const { return val(); }
inline constexpr friend bool operator==(const MontgomeryModInt &x, const MontgomeryModInt &y) { return x.val() == y.val(); }
inline constexpr friend bool operator!=(const MontgomeryModInt &x, const MontgomeryModInt &y) { return x.val() != y.val(); }
inline constexpr MontgomeryModInt &operator=(const MontgomeryModInt &x) & { v = x.v; return *this; }
inline constexpr MontgomeryModInt &operator++() & { return *this += 1; }
inline constexpr MontgomeryModInt operator++(int) & { MontgomeryModInt x = *this; *this += 1; return x; }
inline constexpr MontgomeryModInt &operator--() & { return *this -= 1; }
inline constexpr MontgomeryModInt operator--(int) & { MontgomeryModInt x = *this; *this -= 1; return x; }
inline constexpr MontgomeryModInt operator-()const { return MontgomeryModInt(v ? P2 - v : 0, 0); }
inline constexpr MontgomeryModInt &operator+=(const MontgomeryModInt &x) & { v += x.v, ( v - P2 ) >> ( sizeof(U) * 8 - 1 ) || ( v -= P2 ); return *this; }
inline constexpr MontgomeryModInt &operator-=(const MontgomeryModInt &x) & { v -= x.v, v >> ( sizeof(U) * 8 - 1 ) && ( v += P2 ); return *this; }
inline constexpr MontgomeryModInt &operator*=(const MontgomeryModInt &x) & { v = reduce((D)v * x.v); return *this; }
inline constexpr MontgomeryModInt &operator/=(const MontgomeryModInt &x) & { return *this *= x.inv(); }
inline constexpr friend MontgomeryModInt operator+(MontgomeryModInt x, const MontgomeryModInt &y) { return x += y; }
inline constexpr friend MontgomeryModInt operator-(MontgomeryModInt x, const MontgomeryModInt &y) { return x -= y; }
inline constexpr friend MontgomeryModInt operator*(MontgomeryModInt x, const MontgomeryModInt &y) { return x *= y; }
inline constexpr friend MontgomeryModInt operator/(MontgomeryModInt x, const MontgomeryModInt &y) { return x /= y; }
template < class T, enable_if_t < numeric_limits < T >::is_integer, int > = 0 > inline constexpr MontgomeryModInt qpow(T y)const { MontgomeryModInt x = *this, z = 1; while ( y ) { if ( y & 1 ) z *= x; if ( y >>= 1 ) x *= x; } return z; }
template < class T, enable_if_t < numeric_limits < T >::is_integer, int > = 0 > inline constexpr friend MontgomeryModInt qpow(const MontgomeryModInt &x, T y) { return x.qpow(y); }
inline constexpr MontgomeryModInt inv()const { return qpow(P - 2); }
inline constexpr friend MontgomeryModInt inv(const MontgomeryModInt &x) { return x.inv(); }
inline friend istream &operator>>(istream &is, MontgomeryModInt &x) { S y; is >> y, x = y; return is; }
inline friend ostream &operator<<(ostream &os, const MontgomeryModInt &x) { return os << x.val(); }
};
using mint = MontgomeryModInt<mod>;
using vmi = vector<mint>;
template<class T>
struct matrix {
int n, m;
vector<vector<T>> a;
matrix(int n = 0, int m = 0): n(n), m(m) {
a.assign(n, vector<T>(m));
}
matrix(const vector<vector<T>> &b) {
a = b;
n = sz(a); m = sz(a[0]);
}
friend istream& operator>>(istream& in, matrix &b) {in >> b.a; return in;}
friend ostream& operator<<(ostream& out, const matrix &b) {out << b.a; return out;}
auto& operator[](int i) {return a[i];}
const auto& operator[](int i) const {return a[i];}
static matrix single(int k) {
matrix b(k, k);
while (k--) b[k][k] = 1;
return b;
}
matrix operator*(const matrix &b) const {
matrix c(n, b.m);
for (int i = 0; i < n; ++i) for (int k = 0; k < m; ++k) for (int j = 0; j < b.m; ++j) c[i][j]+=a[i][k]*b[k][j];
return c;
}
matrix operator+(const matrix &b) const {
matrix c(n, m);
for (int i = 0; i < n; ++i) for (int j = 0; j < m; ++j) c[i][j] = a[i][j] + b[i][j];
return c;
}
matrix operator-(const matrix &b) const {
matrix c(n, m);
for (int i = 0; i < n; ++i) for (int j = 0; j < m; ++j) c[i][j] = a[i][j] - b[i][j];
return c;
}
matrix pow(ll k) const {
matrix x = single(n), b = a;
for (; k; k>>=1, b = b*b) if (k & 1) x = x*b;
return x;
}
};
using mat = matrix<mint>;
constexpr int N = 100001;
int n; ll d;
vi g[N];
bool f[N], w[N];
int c[N], a[N], s[N];
void dfs1(int u, int p) {
f[u] = s[u] = a[u] = 0;
trav(v,g[u]) if (v != p) dfs1(v, u), f[u]|=!f[v], s[u]+=!f[v];
if (f[u] && s[u] == 1) {
trav(v,g[u]) if (v != p && !f[v]) a[u]+=a[v];
} else if (!f[u]) {
++a[u];
trav(v,g[u]) if (v != p && f[v]) a[u]+=a[v];
}
}
void dfs(int u, int p) {
w[u] = f[u], c[u] = a[u];
int x = 0, y = 0;
trav(v,g[u]) if (v != p) {
if (f[v]) x+=a[v];
else y+=a[v];
}
trav(v,g[u]) if (v != p) {
int fu = f[u], fv = f[v], su = s[u], sv = s[v], au = a[u], av = a[v];
//delete v from u
if (f[u]) {
if (!f[v]) {
if (s[u] == 1) f[u] = 0, a[u] = x + 1;
else if (s[u] == 2) a[u] = y - a[v];
}
} else a[u]-=a[v];
s[u]-=!f[v];
//add u to v
s[v]+=!f[u];
if (!f[v]) {
if (!f[u]) f[v] = 1, a[v] = a[u];
else a[v]+=a[u];
} else {
if (s[v] > 1) a[v] = 0;
}
dfs(v, u);
f[u] = fu, f[v] = fv, s[u] = su, s[v] = sv, a[u] = au, a[v] = av;
}
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(NULL); cout.tie(NULL);
cout << fixed << setprecision(10);
cin >> n >> d;
if (n == 2) return cout << mint(4).qpow(d), 0;
For(i,1,n){
int u, v; cin >> u >> v;
g[u].pb(v), g[v].pb(u);
}
dfs1(1, 0), dfs(1, 0);
ll e = 0;
FOR(i,1,n){
if (w[i]) e+=c[i];
else e-=c[i];
}
int L = 0;
FOR(i,1,n) L+=!w[i];
mint x = L;
For(i,1,d) x = x*e + mint(n).qpow(2*i)*L;
if (w[1]) x*=c[1];
else x = mint(n).qpow(2*d) - c[1]*x;
cout << mint(n).qpow(2*d) - x;
cerr << "\nProcess returned 0 (0x0) execution time : " << 1.0*clock()/CLOCKS_PER_SEC << " s";
return 0;
}
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