#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")

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

#define ll long long
#define ld long double

const int N = 1e6 + 15, mod = 1e9 + 7;

int n, cat, m;
vector<int> g[N];
int ind[N], in[N], out[N], T = 2, p[N];
vector<int> tour;
void dfs(int node, int par) {
    p[node] = par;
    in[node] = out[node] = tour.size();
    for(auto i : g[node]) {
        if(i != par) {
            ind[i] = out[node] = T++;
            tour.push_back(i);
        }
    }
//    out[node] = tour.size() - 1;
    for(auto i : g[node]) {
        if(i != par)
            dfs(i, node);
    }
}

ld BIT[N];
void add(int i, ld val) {
    for(;i <= n + 10;i += i & -i)
        BIT[i] += val;
}

ld query(int i) {
    ld sum = 0;
    for(;i;i -= i & -i)
        sum += BIT[i];
    return sum;
}

void update(int l, int r, ld val) {
    add(l, val);
    add(r + 1, -val);
}

void init() {
    for(int i = 0;i <= n + 10;i++) {
        g[i].clear();
        BIT[i] = 0;
    }
    tour.clear();
    T = 2;
    tour.push_back(0);
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    string yes = "TAK", no = "NIE";

    int tt;
    cin >> tt;
    while (tt--) {
        cin >> n >> cat;
        init();
        for(int i = 1;i < n;i++) {
            int u, v;
            cin >> u >> v;
            g[u].push_back(v);
            g[v].push_back(u);
        }
        // update 1
        p[1] = 0;
        tour.push_back(1);
        ind[1] = 1;
        dfs(1, 1);
        update(ind[cat], ind[cat], 1);
        cin >> m;
        ld ans = 0;
        for(int i = 0;i < m;i++) {
            int node;
            cin >> node;
            ld k = g[node].size();
            ld cur = query(ind[node]);
            ans += cur;
            update(in[node], out[node], cur / k);
            if(node != 1)
                update(ind[p[node]], ind[p[node]], cur / k);
            update(ind[node], ind[node], -cur);
        }
        cout << fixed << setprecision(10) << ans << '\n';
    }

    return 0;
}