#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>
#include <atcoder/modint>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

using mint = atcoder::modint998244353;

ostream& operator<<(ostream& os, const mint& m){
    os << m.val();
    return os;
}


#define N_MAX 200002
mint inv[N_MAX],fac[N_MAX],finv[N_MAX];

void init(){
    const ll MOD = mint::mod();
    fac[0]=1;fac[1]=1;
    finv[0]=1;finv[1]=1;
    inv[1]=1;
    for(int i=2;i<N_MAX;i++){
        inv[i]=mint(MOD)-inv[MOD%i]*(MOD/i);
        fac[i]=fac[i-1]*(ll) i;
        finv[i]=finv[i-1]*inv[i];
    }
}

mint comb(ll n, ll r){
    if(n < r){
        return mint(0);
    }else{
        return fac[n]*finv[r]*finv[n-r];
    }
}


int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    init();
    int n, c; cin >> n >> c;
    vector<vector<int>> g(n);
    for(int i = 0; i < n-1; i++){
        int a, b; cin >> a >> b; a--; b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    auto sub_solve = [&](int c){
        mint inv_c = mint(c).inv();
        mint ans = 1;
        for(int v = 0; v < n; v++){
            int deg = g[v].size();
            mint tmp = c;
            mint n_all = mint(c).pow(deg);
            mint more_than_half = 0;
            for(int x = deg; x*2 > deg; x--){
                more_than_half += comb(deg, x)*c*(mint(c-1).pow(deg-x));
            }
            tmp += n_all-more_than_half;
            if(v != 0) tmp *= inv_c;
            // cout << deg << ":" << tmp << endl;
            ans *= tmp;
        }
        return ans;
    };
    vector<mint> v(c+1);
    for(int cc = 1; cc <= c; cc++){
        v[cc] = sub_solve(cc);
    }
    for(int cc = 1; cc <= c; cc++){
        for(int x = 1; x < cc; x++){
            v[cc] -= v[x]*comb(cc, x);
        }
    }
    cout << v[c] << endl;
}