#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#ifdef APURBA
#include "DEBUG_TEMPLATE.h"
#else
#define HERE
#define debug(args...)
#endif
#define ALL(x) x.begin(),x.end()
const int M=5e6+5,N=1e6+5;

int n;
vector<int>e[N];
bool vis[M];
int m;
vector<int>all;
ld dp[M];
vector<int>pos[N];

ld run(int idx)
{
    if(idx>=5000)
        return 0;
    if(vis[idx]==1)
        return dp[idx];

    int node=all[idx];

    vis[idx]=1;
    ld sum=0;
    for(int u:e[node])
    {
        auto itr=lower_bound(pos[u].begin(),pos[u].end(),idx);
        if(itr!=pos[u].end())
        {
            sum+=(1+run(*itr));
        }
    }
    sum/=(int)e[node].size();
    return dp[idx]=sum;
}

void TEST_CASES()
{
    int c;
    cin>>n>>c;
    for(int i=1;i<=n;i++)
        pos[i].clear(),e[i].clear();

    for(int i=0;i<n-1;i++)
    {
        int u,v;
        cin>>u>>v;
        e[u].push_back(v);
        e[v].push_back(u);
    }



    cin>>m;
    all.resize(m);
    for(int i=0;i<m;i++)
    {
        vis[i]=0;
        cin>>all[i];
        pos[all[i]].push_back(i);
    }

    if(pos[c].size()==0)
    {
        cout<<0<<"\n";
    }
    else {
        cout<<fixed<<setprecision(10)<<1+run(pos[c][0])<<"\n";
    }


}


/*
*/

int32_t main()
{
#ifndef APURBA
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
#endif
    //freopen("input.txt","r",stdin);
    //freopen("out1.txt","w",stdout);
    int t=1;
    cin>>t;
    while(t--)
    {
        TEST_CASES();
    }
    return 0;
}