#include <bits/stdc++.h>
using namespace std;

#define cs const
#define pb push_back

cs int N = 1e6 + 5;
cs int M = 5e6 + 5;

int T; 
int n, m, C; 
vector <int> e[N], ee[N];
int c[N];
int a[M];

double sum[N];
double dp[N];

void clear() {
    for(int i = 0; i <= n; i++) 
        sum[i] = dp[i] = 0, e[i].clear(), ee[i].clear(), c[i] = 0; 
}

void Main() {
    cin >> n >> C; 
    for(int i = 1; i < n; i++) {
        int x, y; 
        cin >> x >> y; 
        e[x].pb(y);
        e[y].pb(x);
    }
    cin >> m; 
    for(int i = 1; i <= m; i++) {
        cin >> a[i];
        ++ c[a[i]];
    }
    int B = sqrt(m) / 2; 
    B = max(B, 10); 

    for(int i = 1; i <= n; i++) {
        for(int v : e[i]) {
            if(c[v] > B) {
                ee[i].pb(v);
            }
        }
    }

    for(int i = m; i; i--) {
        int x = a[i];
        for(int v : ee[x]) sum[v] -= dp[x];
        if(c[x] > B) {
            dp[x] = sum[x] / (e[x].size()) + 1; 
        }
        else {
            double s = 0; 
            for(int v : e[x]) s += dp[v];
            dp[x] = s / e[x].size() + 1; 
        }
        for(int v : ee[x]) sum[v] += dp[x];
    }
    printf("%.10lf\n", dp[C]);
}

int main() {
    #ifdef zqj
    freopen("1.in","r",stdin);
    #endif 
    ios :: sync_with_stdio(0), cin.tie(0);
    cin >> T; 
    while(T--) Main(), clear();
    return 0; 
}