#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")
#include <iostream>
#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define fi first
#define sc second
#define EPS 1e-9
#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>

#define EPS 1e-9
#define PI acos(-1.0)
#define ll long long
#define all(s) s.begin(),s.end()
#define rall(s) s.rbegin(),s.rend()
#define pb push_back
#define ft first
#define sc second
#define pi pair<ll,ll>
#define vi vector<ll>
#define sz(s) s.size()
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
typedef tree<ll, null_type, less<ll>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
const ll N = 1e6+5, M = 300 + 5, MOD = 1e4+5, INF = 1e18;
int dx[] = {-1, 1, 0, 0}, Dx[] = {-1, -1, 0, 1, 1, 1, 0, -1};;
int dy[] = {0, 0, 1, -1}, Dy[] = {0, 1, 1, 1, 0, -1, -1, -1};
int n, m, tt, ID[N], timer, mx[N],p[N];
vi g[N];
long double seg[N*4], lazy[N*4];
void bfs(int s)
{
    queue<int> q;
    q.push(s);
    ID[s] = ++timer;
    while(sz(q))
    {
        int node = q.front(); q.pop();
        for(auto it:g[node])
        {
            if(!ID[it]){
                ID[it] = ++timer;
                q.push(it);
                p[it]=s;
            }
        }
    }
}
void dfs(int s,int p)
{
    int tmp = ID[s];
    for(auto it:g[s])
    {
        tmp = max(tmp,ID[it]);
    }
    mx[s] = tmp;
    for(auto it:g[s])
    {
        if(it != p)
        {
            dfs(it,s);
        }
    }
}
void check(int v,int l,int r)
{
    if(lazy[v]>EPS)
    {
        seg[v] = lazy[v];
        if(l != r){
            lazy[v*2] += lazy[v];
            lazy[v*2+1] += lazy[v];
        }
        lazy[v] = 0;
    }
}
void update(int v,int l,int r,int s,int e,long double val)
{
    check(v,l,r);
    if(l >= s && r <= e)
    {
        lazy[v] += val;
        check(v,l,r);
        return;
    }
    if(l > e || r < s) return;
    int mid = (l+r) / 2;
    update(v*2,l,mid,s,e,val);
    update(v*2+1,mid+1,r,s,e,val);
    seg[v] = seg[v*2] + seg[v*2+1];
}
long double get(int v,int l,int r,int s,int e)
{
    check(v,l,r);
    if(l > e || r < s) return 0;
    if(l >= s && r <= e) return seg[v];
    int mid = (l+r) / 2;
    return get(v*2,l,mid,s,e) + get(v*2+1,mid+1,r,s,e);
}
int main()
{
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);

	int t;
	cin>>t;
	while(t--)
    {
        int c;
        cin >> n;
        cin >> c;
        memset(ID,0,sizeof ID);
        memset(mx,0,sizeof mx);
        for(int i=0;i<=n+1;i++)g[i].clear();
        memset(lazy,0,sizeof lazy);
        for(int i = 1; i < n;++i)
        {
            int u , v;
            cin >> u >> v;
            g[u].pb(v);
            g[v].pb(u);
        }
        bfs(1);
        dfs(1,1);
        update(1,1,n,ID[c],ID[c],1);
        int m;
        cin>>m;
        long double ans=0;
        cout<<fixed<<setprecision(10);
        for(int i=0;i<m;i++)
        {
            int room;
            cin>>room;
            long double cur=get(1,1,n,ID[room],ID[room]);
            ans+=cur;
            ///update childs
            update(1,1,n,mx[room]-g[room].size()+1,mx[room],cur/g[room].size());
            update(1,1,n,ID[p[room]],ID[p[room]],cur/g[room].size());
            ///update room
            update(1,1,n,ID[room],ID[room],-cur);

        }
        cout<<ans<<'\n';
    }

	return 0;
}
/*
2
3 3 1
.XX
XXX
XX.
3 4 1
..XX
X.XX
X..X
*/