GGBHAI

#include<iostream>
#include<vector>
#include<queue>
#include<cstdio>
#define ll long int
using namespace std;
int main() {
    int t;
    scanf("%d", &t);
    while(t--) {
        ll n, m, u, v;
        scanf("%ld%ld", &n, &m);
        vector< vector<ll> > a(n);
        vector<ll> level(n);
        for(ll i = 0; i < n-1; i++) {
            scanf("%ld%ld", &u, &v);
            u--; v--;
            a[u].push_back(v);
            a[v].push_back(u);
        }
        vector<bool> isRestaurant(n, false);
        for(ll i = 0; i < m; i++) {
            scanf("%ld", &u);
            u--;
            isRestaurant[u] = true;
        }
        queue<ll> q;
        q.push(0);
        ll l = 0;
        level[0] = 0;
        vector<bool> visited(n, false);
        ll total = 0;
        do {
            queue<ll> q1;
            while(!q.empty()) {
                ll node = q.front();
                q.pop();
                level[node] = l;
                if(isRestaurant[node]) {
                    total += 2*l;
                }
                visited[node] = true;
                for(vector<ll>::iterator it = a[node].begin(); it != a[node].end(); ++it) {
                    if(!visited[*it])
                        q1.push(*it);
                }
            }
            l++;
            q = q1;
        }while(!q.empty());
        double ans = 1.0/m * total;
        printf("%.6f\n", ans);
    }
    return 0;
}