#include <bits/stdc++.h>
using namespace std;
const int N = 100001;
vector<int> e[N];
int fa[N];
double f[N], g[N];

void dfs(int x, int fa) {
  ::fa[x] = fa;
  for (auto v : e[x]) {
    if (v != fa)
      dfs(v, x);
  }
}

void set_dpv(int x, double val) {
  if (fa[x] != -1)
    g[fa[x]] -= f[x];
  f[x] = val;
  if (fa[x] != -1)
    g[fa[x]] += f[x];
};

double get_val(int u) {
  double res = g[u];
  if (fa[u] != -1)
    res += f[fa[u]];
  return res;
};

void solve() {
  int n, c;
  scanf("%d%d", &n, &c);

  for (int i = 0; i < n - 1; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    e[x].push_back(y);
    e[y].push_back(x);
  }
  dfs(1, 0);
  int m;
  scanf("%d", &m);
  vector<int> s;
  for (int i = 1; i <= m; i++) {
    int x;
    scanf("%d", &x);
    s.push_back(x);
  }

  for (int i = m - 1; i >= 0; i--) {
    int x = s[i];
    double w = get_val(x) / (double)e[x].size() + 1;
    set_dpv(x, w);
  }

  printf("%.12lf\n", f[c]);
}

int main() {
  int T;
  scanf("%d", &T);
  while (T--) {
    solve();
  }
}