#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define pb push_back
#define ff first
#define ss second
const int mod = 1e9 + 7;
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n; ll d; cin>>n>>d;
vector<int> g[n + 1];
for (int i = 1; i < n; i++){
int u, v; cin>>u>>v;
g[u].pb(v);
g[v].pb(u);
}
vector<int> p(n + 1), h(n + 1);
function<void(int, int)> fill = [&](int v, int pr){
p[v] = pr; h[v] = 1;
for (int i: g[v]){
if (i == pr) continue;
fill(i, v);
h[v] = min(h[v], h[i]);
}
h[v] = !h[v];
};
vector<vector<bool>> f(n + 1, vector<bool>(2));
function<void(int)> dfs = [&](int v){
int s = 0, x = 0;
for (int i: g[v]){
if (i == p[v]) continue;
if (!h[i]){
s++;
x = i;
}
}
for (int i: g[v]){
if (i == p[v]) continue;
f[i][0] = f[v][1];
if (!s || (s == 1 && i == x)){
f[i][1] = f[v][0];
}
else {
f[i][1] = f[v][1];
}
dfs(i);
}
};
vector<vector<int>> dp(n + 1, vector<int>(2));
for (int i = 1; i <= n; i++){
fill(i, 0);
dp[i][h[i]] = 1;
}
vector<vector<int>> dp1(n + 1, vector<int>(2));
for (int v = 1; v <= n; v++){
fill(v, 0);
f[v][0] = 0; f[v][1] = 1;
dfs(v);
int s1 = 0, s0 = 0;
for (int x = 1; x <= n; x++){
s1 = (s1 + dp[x][1]) % mod;
s0 = (s0 + dp[x][0]) % mod;
}
for (int x = 1; x <= n; x++){
dp1[v][h[v]] = (dp1[v][h[v]] + s1) % mod;
dp1[v][f[x][1]] = (dp1[v][f[x][1]] + s0) % mod;
}
}
dp = dp1;
cout<<dp[1][1]<<"\n";
}
