#include <stdio.h>

const int Mod = 998244353;
long long fact[100001], fact_inv[100001], pow[2][100001];

long long div_mod(long long x, long long y, long long z)
{
	if (x % y == 0) return x / y;
	else return (div_mod((1 + x / y) * y - x, (z % y), y) * z + x) / y;
}

long long combination(int n, int k)
{
	return fact[n] * fact_inv[k] % Mod * fact_inv[n-k] % Mod;
}

typedef struct List {
	struct List *next;
	int v;
} list;

long long solve(int N, int C, list* adj[])
{
	if (C == 1) return 1;
	
	int i, r = 1, u, w, head, tail;
	static int par[100001] = {}, q[100001];
	list *p;
    if (par[r] == 0) {
		par[r] = r;
		q[0] = r;
		for (head = 0, tail = 1; head < tail; head++) {
			u = q[head];
			for (p = adj[u]; p != NULL; p = p->next) {
				w = p->v;
				if (par[w] == 0) {
					par[w] = u;
					q[tail++] = w;
				}
			}
		}
	} else head = N;

	int k;
	static long long dp[100001], prod;
	for (head--; head > 0; head--) {
		u = q[head];
		for (p = adj[u], k = 0, prod = 1; p != NULL; p = p->next) {
			w = p->v;
			if (w == par[u]) continue;
			prod = prod * dp[w] % Mod;
			k++;
		}
		dp[u] = pow[0][k];
		for (i = (k + 1) / 2; i < k; i++) dp[u] += Mod - combination(k, i) * pow[1][k-i] % Mod;
		for (i = (k + 3) / 2; i <= k; i++) dp[u] += Mod - combination(k, i) * pow[1][k-i+1] % Mod;
		dp[u] = dp[u] % Mod * prod % Mod;
	}
	for (p = adj[r], k = 0, prod = 1; p != NULL; p = p->next) {
		w = p->v;
		prod = prod * dp[w] % Mod;
		k++;
	}
	dp[r] = pow[0][k-1];
	for (i = k / 2 + 1; i < k; i++) dp[r] += Mod - combination(k, i) * pow[1][k-i] % Mod;
	return dp[r] % Mod * prod % Mod * C % Mod;
}

int main()
{
	int i, k, N, C, u, w;
    list *adj[100001] = {}, e[200001];
	scanf("%d %d", &N, &C);
	for (i = 0; i < N - 1; i++) {
		scanf("%d %d", &u, &w);
		e[i*2].v = w;
		e[i*2+1].v = u;
		e[i*2].next = adj[u];
		e[i*2+1].next = adj[w];
		adj[u] = &(e[i*2]);
		adj[w] = &(e[i*2+1]);
	}
	for (i = 1, fact[0] = 1; i <= N; i++) fact[i] = fact[i-1] * i % Mod;
	for (i = N - 1, fact_inv[N] = div_mod(1, fact[N], Mod); i >= 0; i--) fact_inv[i] = fact_inv[i+1] * (i + 1) % Mod;
	for (k = 1, pow[1][0] = 1; k <= N; k++) pow[1][k] = pow[1][k-1] * C % Mod;
	
	long long ans = 0;
	for (i = C; i >= 1; i--) {
		for (k = 0; k <= N; k++) pow[0][k] = pow[1][k];
		for (k = 1, pow[1][0] = 1; k <= N; k++) pow[1][k] = pow[1][k-1] * (i - 1) % Mod;
		if ((C - i) % 2 == 0) ans += solve(N, i, adj) * combination(C, i) % Mod;
		else ans += Mod - solve(N, i, adj) * combination(C, i) % Mod;
	}
	printf("%lld\n", ans % Mod);
	fflush(stdout);
	return 0;
}