#include<bits/stdc++.h>
#define M 1000005
using namespace std;
int n, c, fa[M];
double tg[M], ori[M], gt[M];
vector<int> v[M];
void dfs(int x, int ft)
{
	fa[x] = ft;
	for(auto &t : v[x])
	{
		if(t == ft) continue;
		dfs(t, x);
	}
}
void solve()
{
	scanf("%d%d", &n, &c);
	for(int i = 1; i <= n; i++) ori[i] = 0, gt[i] = 0, tg[i] = 0, v[i].clear();
	for(int i = 1, x, y; i < n; i++) scanf("%d%d", &x, &y), v[x].push_back(y), v[y].push_back(x);
	dfs(1, 0);
	ori[c] = 1;
	int m;
	scanf("%d", &m); 
	double ans = 0;
	for(int i = 1, x; i <= m; i++)
	{
		scanf("%d", &x);
		double nw = ori[x] + tg[fa[x]] - gt[x];
		gt[x] = tg[fa[x]];
		ori[x] = 0;
		ans += nw;
		nw /= v[x].size();
		ori[fa[x]] += nw;
		tg[x] += nw;
	}
	printf("%.10lf", ans);
}
int main()
{
	int T;
	scanf("%d", &T);
	while(T--) solve(); 
	return 0;
}