#include <bits/stdc++.h>
    
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

mt19937 rng((int) chrono::steady_clock::now().time_since_epoch().count());
    
const int MOD = 1e9 + 7;
const int MAXN = 1e6 + 5;
const int INF = 1e9;

int sq, room[5 * MAXN];
double dp[MAXN], keep[MAXN];
vector<int> v[MAXN], big[MAXN];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(20) << fixed;
    int t;
    cin >> t;
    while (t--) {
        int n, m, c;
        cin >> n >> c;
        sq = sqrt(n);
        int a, b;
        for (int i = 0; i < n - 1; i++) {
            cin >> a >> b;
            v[a].push_back(b);
            v[b].push_back(a);
        }
        for (int i = 1; i <= n; i++) {
            for (int x : v[i]) {
                if (v[x].size() > sq) big[i].push_back(x);
            }
        }
        cin >> m;
        for (int i = 0; i < m; i++) {
            cin >> room[i];
        }
        double ans = 0;
        for (int i = m - 1; i >= 0; i--) {
            double ant = dp[room[i]];
            double sum = keep[room[i]];
            for (int x : big[room[i]]) {
                sum += dp[x];
            }
            dp[room[i]] = 1 + sum / v[room[i]].size();
            if (v[room[i]].size() <= sq) {
                // big
                for (int x : v[room[i]]) {
                    keep[x] += dp[room[i]] - ant;
                }
            }
            if (room[i] == c) ans = dp[room[i]];
        }
        cout << ans << '\n';
        for (int i = 1; i <= n; i++) {
            dp[i] = 0;
            keep[i] = 0;
            v[i].clear();
            big[i].clear();
        }
    }
    return 0;
}