#include <bits/stdc++.h>

#define ndl '\n'
#define ll long long
#define INF 1000000007
#define st first
#define nd second
#define debug(x) cout << #x << ": " << x << ndl
#define pb push_back
#define pob pop_back
#define pf push_front
#define pof pop_front
#define lb lower_bound
#define ub upper_bound
#define all(x) (x).begin(), (x).end()

using namespace std;

void rob() {
    int n, c; cin>>n>>c;
    vector<vector<int>> G(n+1);
    vector<long double> chance(n+1), lazy_propagation(n+1);    
    chance[c] = 1;

    for(int i=0;i<n-1;i++) {
        int a, b; cin>>a>>b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    vector<int> par(n+1);
    function<void(int)> dfs = [&](int v) {
        for(auto x:G[v]) {
            if(x != par[v]) {
                par[x] = v;
                dfs(x);
            }
        }
    };

    dfs(1);

    long double ans = 0;

    function<long double(int)> full_chance = [&](int x) -> long double {
        return chance[x] + (par[x] ? lazy_propagation[par[x]] : 0.0);
    };

    int seq; cin>>seq;
    for(int i=0;i<seq;i++) {
        int curr; cin>>curr;

        long double curr_chance = full_chance(curr);
        chance[curr] -= curr_chance;
        ans += curr_chance;

        lazy_propagation[curr] += curr_chance / G[curr].size();
        if(par[curr]) {
            chance[par[curr]] += curr_chance / G[curr].size();
        }
        
    }
    cout<<ans<<'\n';
}

int main() {
    cout<<setprecision(8) << fixed;
    ios_base::sync_with_stdio(0); cin.tie(0);
    int t;
    cin>>t;
    for(int i=0;i<t;i++)
        rob();
}