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

// #pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx2")
#define forn(i,a,b) for(int i=(a); (i)<(b); i++)
#define fore(i,a,b) for(int i=(a); (i)<=(b); i++)
#define pb push_back
#define sz(a) static_cast<int>((a).size())
#define F first
#define S second
constexpr int INF = 1'000'000'000;
using ll = long long;
using ld = double;

struct FT {
    vector<ld> s;
    FT(int n) : s(n) {}
    void update0(int pos, ld dif) {
        if (pos < 0 || pos >= sz(s)) return;
        for (; pos < sz(s); pos |= pos + 1) s[pos] += dif;
    }
    void update(int l, int r, ld dif) {
        if (l > r) return;
        update0(l, dif);
        update0(r + 1, -dif);
    }
    ld query(int pos) { // sum of values in [0, pos]
        pos++;
        ld res = 0;
        for (; pos > 0; pos &= pos - 1) res += s[pos-1];
        return res;
    }
};

void solve()
{
    int n; cin>>n;
    int c; cin>>c; c--;
    vector<vector<int>> adj(n);
    forn(i,0,n-1)
    {
        int u,v; cin>>u>>v; u--; v--;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    int m; cin>>m;
    vector<int> a(m);
    forn(i,0,m)
    {
        cin>>a[i];
        a[i]--;
    }

    int tmr=-1;
    vector<int> prt(n, -1);
    vector<int> in(n), out(n);

    vector<bool> vst(n, false);
    queue<int> q;
    q.push(0);
    in[0] = ++tmr;
    vst[0] = 1;
    while(!q.empty())
    {
        int u = q.front(); q.pop();
        for (const int v : adj[u])
        {
            if (vst[v]) continue;
            vst[v] = 1;
            q.push(v);
            prt[v] = u;
            in[v] = ++tmr;
        }
        out[u] = tmr;
    }

    FT fw(n);
    fw.update(in[c], in[c], 1);
    ld ans = 0;
    for(const int x : a)
    {
        ld cur = fw.query(in[x]);
        ans += cur;
        ld upd = cur / sz(adj[x]);
        int p = prt[x];
        fw.update(in[x], in[x], -cur);
        fw.update(in[x] + 1, out[x], upd);
        if (p != -1)
            fw.update(in[p], in[p], upd);
    }
    cout<<setprecision(10)<<fixed;
    cout<<ans<<'\n';
}

int main()
{
    cin.tie(0)->sync_with_stdio(0);

    int t; cin>>t;
    forn(i,0,t) solve();
}