#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
#define INF 1000000000
#define INFl 1000000000000000000
#define all(x) x.begin(), x.end()
#define sajz(x) (int)x.size()
#define pb push_back
#define se second
#define fi first
#define yes puts("YES")
#define no puts("NO")
#define erase_duplicates(x) {sort(all(x));(x).resize(distance((x).begin(), unique(all(x))));}
using namespace std;
//using namespace __gnu_pbds;
void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif

#define int ll

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef set<int> si;
typedef multiset<int> msi;
typedef long double ld;
//typedef cc_hash_table<int, int, hash<int>> ht;

const int N = 1e6 + 5;

long double lazy[N], p[N];
vi adj[N];

void test_case() {
	int n, c;
	cin >> n >> c;

	c --;
	for (int i = 0; i < n; i ++) {
		adj[i].clear();
		lazy[i] = 0;
		p[i] = 0;
	}

	p[c] = 1;

	for (int i = 0; i < n - 1; i ++) {
		int a, b;
		cin >> a >> b;
		a --, b --;
		
		adj[a].pb(b);
		adj[b].pb(a);
	}

	int k;
	cin >> k;
	vi a(k);
	long double ans = 0;
	int parent = -1;
	for (int i = 0; i < k; i ++) {
		cin >> a[i];
		a[i] --;

		if (parent != -1) p[a[i]] += lazy[parent];
		ans += p[a[i]];

		int cnt = sajz(adj[a[i]]);
		lazy[a[i]] += p[a[i]] / cnt;

		debug(i, p[a[i]], lazy[a[i]], cnt);

		p[a[i]] = 0;
		parent = a[i];
	}

	cout << fixed << setprecision(7) << ans << '\n';
}

int32_t main() {
	ios_base::sync_with_stdio(false);
	cout.tie(0);
	cin.tie(0);
	int t=1;
	cin >> t;
	for (int i = 1; i <= t; i ++) {
		test_case();
	}
}