THOUSES

// Problem: Tree House
// Contest: CodeChef - May Challenge 2021 Division 2 (Rated)
// URL: https://www.codechef.com/MAY21B/problems/THOUSES
// Memory Limit: 256 MB
// Time Limit: 1000 ms
// Parsed on: 09-05-2021 18:36:27 IST (UTC+05:30)
// Author: Kapil Choudhary
// ********************************************************************
// कर्मण्येवाधिकारस्ते मा फलेषु कदाचन |
// मा कर्मफलहेतुर्भूर्मा ते सङ्गोऽस्त्वकर्मणि || १.४७ ||
// ********************************************************************

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

#define ll long long
#define ull unsigned long long
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define PI 3.1415926535897932384626
#define deb(x) cout << #x << "=" << x << endl
#define deb2(x, y) cout << #x << "=" << x << ", " << #y << "=" << y << endl
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ull> vull;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef vector<vull> vvull;
mt19937_64 rang(chrono::high_resolution_clock::now().time_since_epoch().count());
int rng(int lim) {
    uniform_int_distribution<int> uid(0,lim-1);
    return uid(rang);
}

const int INF = 0x3f3f3f3f;
const ll mod = 1e9+7;
const int N = 3e5;

vvi g;
vi cnt;
vll val;
vector<bool> vis;
ll res;
int n, x;

void dfs(int cur, int par) {
    cnt[cur] += 1;
    for(auto child: g[cur]) {
        if(child != par) {
            dfs(child, cur);
            cnt[cur] += cnt[child];
        }
    }
}

void bfs() {
    queue<pair<int, ll>> q;
    q.push({1, x});
    vis[1] = 1;

    while(!q.empty()) {
        pair<int, ll> cur = q.front();
        q.pop();
        val[cur.F] = cur.S;

        vpii tmp;
        for(auto child: g[cur.F]) {
            if(!vis[child]) {
                vis[child] = 1;
                tmp.pb({cnt[child], child});
            }
        }

        sort(tmp.rbegin(), tmp.rend());
        for(int i = 0; i < (int)tmp.size(); i++) {
            ll value = cur.S * (i + 1);
            value %= mod;
            q.push({tmp[i].S, value});
        }
    }
}

void solve()
{
    cin >> n >> x;
    g.clear(); g.resize(n + 1);
    cnt.clear(); cnt.resize(n + 1, 0);
    val.clear(); val.resize(n + 1, 0);
    vis.clear(); vis.resize(n + 1, 0);
    res = 0LL;

    for(int i = 0; i < n - 1; i++) {
        int u, v; cin >> u >> v;
        g[u].pb(v);
        g[v].pb(u);
    }

    dfs(1, 0);
    bfs();

    for(int i = 1; i <= n; i++) {
        res = (res + val[i]) % mod;
    }

    cout << res << "\n";
}

int main()
{
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    srand(chrono::high_resolution_clock::now().time_since_epoch().count());

    // #ifndef ONLINE_JUDGE
    //     freopen("input.txt", "r", stdin);
    //     freopen("output.txt", "w", stdout);
    // #endif

    int t = 1;
    // int test = 1;
    cin >> t;
    while(t--) {
      // cout << "Case #" << test++ << ": ";
      solve();
    }

    return 0;
}