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

#define all(x) begin(x), end(x)
#ifdef CKISEKI
#define safe cerr << __PRETTY_FUNCTION__ << " line " << __LINE__ << " safe\n"
#define debug(a...) debug_(#a, a)
#define orange(a...) orange_(#a, a)
template <typename ...T>
void debug_(const char *s, T ...a) {
    cerr << "\e[1;32m(" << s << ") = (";
    int cnt = sizeof...(T);
    (..., (cerr << a << (--cnt ? ", " : ")\e[0m\n")));
}
template <typename I>
void orange_(const char *s, I L, I R) {
    cerr << "\e[1;32m[ " << s << " ] = [ ";
    for (int f = 0; L != R; ++L)
        cerr << (f++ ? ", " : "") << *L;
    cerr << " ]\e[0m\n";
}
#else
#define safe ((void)0)
#define debug(...) safe
#define orange(...) safe
#endif

using llf = double;

constexpr int kN = 1000000;

vector<int> g[kN];
int pa[kN];

void dfs(int u, int f) {
    pa[u] = f;
    for (int v : g[u]) {
        if (v == f)
            continue;
        dfs(v, u);
    }
}

llf v1[kN], v2[kN];

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    int t;
    cin >> t;
    while (t--) {
        int n, c;
        cin >> n >> c;
        for (int i = 1; i < n; ++i) {
            int u, v;
            cin >> u >> v;
            --u, --v;
            g[u].push_back(v);
            g[v].push_back(u);
        }
        dfs(0, -1);
        c -= 1;
        v1[c] = 1;
        llf ans = 0;
        int m;
        cin >> m;
        while (m--) {
            int x;
            cin >> x;

            llf cur = v1[x];
            if (pa[x] != -1) {
                cur += v2[pa[x]];
            }

            v1[x] -= cur;
            v2[x] += cur / g[x].size();
            if (pa[x] != -1) {
                v1[pa[x]] += cur / g[x].size();
            }
            
            ans += cur;
        }
        cout << fixed << setprecision(10) << ans << '\n';

        for (int i = 0; i < n; ++i) {
            g[i].clear();
            v1[i] = v2[i] = 0;
        }
    }
    return 0;
}