/**
	author:  shobonvip
	created: 2025.07.15 18:13:17
**/

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

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)
#define all(v) v.begin(), v.end()

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

//defmodfact
const int COMinitMAX = 998244;
mint fact[COMinitMAX+1], factinv[COMinitMAX+1];

void modfact(){
	fact[0] = 1;
	for (int i=1; i<=COMinitMAX; i++){
		fact[i] = fact[i-1] * i;
	}
	factinv[COMinitMAX] = fact[COMinitMAX].inv();
	for (int i=COMinitMAX-1; i>=0; i--){
		factinv[i] = factinv[i+1] * (i+1);
	}
}

mint cmb(int a, int b){
	if (a<b || b<0) return mint(0);
	return fact[a]*factinv[b]*factinv[a-b];
}
//--------


int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	
	modfact();
	int n, c;
	cin >> n >> c;
	vector ikeru(n, vector<int>(0));
	vector<int> deg(n);
	rep(i,0,n-1){
		int u, v;
		cin >> u >> v;
		u--; v--;
		ikeru[u].push_back(v);
		ikeru[v].push_back(u);
		deg[u]++;
		deg[v]++;
	}


	vector<mint> dp(n);
	mint ans = 0;
	rep(d,1,c+1) {
		mint keis = cmb(c, d) * ((c - d) % 2 == 0 ? 1 : -1);
		rep(i,0,n) {
			mint tmp = mint(d).pow(deg[i]);
			rep(j,deg[i]/2+1,deg[i]) {
				tmp -= cmb(deg[i],j) * mint(d-1).pow(deg[i]-j) * d;
			}
			keis *= tmp;
		}
		ans += keis / mint(d).pow(n-1);
	}
	cout << ans.val() << endl;
}