#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define task "text"
#define fi first
#define se second
const int N = 5e5+5;
vector<int> adj[N];
int c[N],h[N],d[N],vis[N],has[N];
int wharf[N];
int n,k;
void bfs(){
queue<int> q;
for(int i=1;i<=n;i++) d[i]=1e9;
for(int i=1;i<=k;i++){
d[c[i]]=0;
q.push(c[i]);
}
while(!q.empty()){
int u=q.front();
q.pop();
for(int v:adj[u]){
if(d[v]>d[u]+1){
d[v]=d[u]+1;
q.push(v);
}
}
}
}
void dfs(int u,int p,int now){
h[u]=h[p]+1;
if(h[u]+d[u] > h[now]+d[now]){
now=u;
}
wharf[u]=now;
for(int v:adj[u]){
if(v==p) continue;
dfs(v,u,now);
}
}
map<pair<int,int>,int> mp;
int findid(int u,int v){
if(u>v) swap(u,v);
return mp[{u,v}];
}
signed main(){
ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
if(fopen(task".inp","r")){
freopen(task".inp","r",stdin);
//freopen(task".out","w",stdout);
}
cin>>n>>k;
for(int i=1;i<n;i++){
int u,v;
cin>>u>>v;
adj[u].push_back(v);
adj[v].push_back(u);
if(u>v) swap(u,v);
mp[{u,v}]=i;
}
for(int i=1;i<=k;i++) cin>>c[i];
bfs();
dfs(1,0,0);
set<pair<int,int>> s;
for(int i=1;i<=k;i++){
int u=c[i];
has[u]=1;
s.insert({h[u],u});
}
int ans=0;
vector<int> vec;
//cerr<<wharf[1]<<' '<<wharf[4]<<'\n';
for(int i=1;i<=k;i++){
//cerr<<c[i]<<' '<<wharf[c[i]]<<'\n';
}
while(!s.empty()){
ans++;
int u=s.rbegin()->se;
//cerr<<u<<'\n';
queue<pair<int,int>> q;
int dis=h[u]-h[wharf[u]];
u=wharf[u];
vec.push_back(u);
q.push({u,0});
while(!q.empty()){
int u=q.front().fi;
int di=q.front().se;
q.pop();
if(has[u]){
if(s.find({h[u],u}) != s.end()) s.erase(s.find({h[u],u}));
}
if(di == dis) continue;
for(int v:adj[u]){
int id=findid(u,v);
if(!vis[id]){
vis[id]=1;
q.push({v,di+1});
}
}
}
}
cout<<ans<<'\n';
for(int v:vec) cout<<v<<' ';
}
