using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	class Pair{
		public int Idx, Dep;
		public Pair(int idx, int dep){
			Idx = idx; Dep = dep;
		}
	}
	public void Solve(){
		if(N == 1){
			Console.WriteLine(K);
			return;
		}
		
		List<int>[] E = new List<int>[N];
		for(int i=0;i<N;i++) E[i] = new List<int>();
		for(int i=0;i<N-1;i++){
			E[A[i]].Add(B[i]);
			E[B[i]].Add(A[i]);
		}
		
		int[] depth = new int[N];
		for(int i=0;i<N;i++) depth[i] = -1;
		var q = new Queue<int>();
		
		mlong ans = K;
		q.Enqueue(0);
		depth[0] = 0;
		while(q.Count > 0){
			var now = q.Dequeue();
			int ccnt = now == 0 ? E[now].Count : (E[now].Count - 1);
			int clr = now == 0 ? K - 1 : K - 2;
			if(clr < ccnt) {
				Console.WriteLine(0);
				return;
			}
			ans *= Perm(clr, ccnt);
			foreach(var nxt in E[now]){
				if(depth[nxt] == -1){
					depth[nxt] = depth[now] + 1;
					q.Enqueue(nxt);
				}
			}
		}
		
		Console.WriteLine(ans);
		
	}
	
	mlong[][] memo;
	bool Init = false;
	mlong Perm(int clr, int ccnt){
		if(!Init){
			Init = true;
			memo = new mlong[2][];
			memo[0] = new mlong[K + 2];
			memo[1] = new mlong[K + 2];
			memo[0][0] = 1;
			memo[1][0] = 1;
			for(int i=1;i<K+2;i++){
				memo[0][i] = memo[0][i-1] * (K - 1 - (i - 1));
				memo[1][i] = memo[1][i-1] * (K - 2 - (i - 1));
			}
		}
//Console.WriteLine("clr:{0}, ccnt:{1},Init:{2}. ret:{3}",clr,ccnt,Init,memo[(K - 1) - clr][ccnt]);
		return memo[(K - 1) - clr][ccnt];
		
	}
	
	
	
	int N,K;
	int[] A,B;
	public Sol(){
		var d = ria();
		N = d[0];
		K = d[1];
		A = new int[N-1];
		B = new int[N-1];
		for(int i=0;i<N-1;i++){
			d = ria();
			A[i] = d[0] - 1;
			B[i] = d[1] - 1;
		}
	}

	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(char sep=' '){return Console.ReadLine().Split(sep);}
	static int[] ria(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>int.Parse(e));}
	static long[] rla(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>long.Parse(e));}
	static double[] rda(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>double.Parse(e));}
}


struct mlong {
	
	const long mod = (long) 1e9 + 7;
	long V;
	
	public mlong(long _v = 0){
		V = _v;
	}
	
	public static mlong operator+(mlong a, mlong b){
		var v0 = a.V + b.V; if(v0 >= mod) v0 -= mod;
		return new mlong(v0);
	}
	public static mlong operator-(mlong a, mlong b){
		var v0 = mod + a.V - b.V; if(v0 >= mod) v0 -= mod;
		return new mlong(v0);
	}
	public static mlong operator*(mlong a, mlong b){
		var v0 = a.V * b.V; if(v0 >= mod) v0 %= mod;
		return new mlong(v0);
	}
	public static mlong operator/(mlong a, mlong b){
		var v0 = a.V * inv(b.V).V; if(v0 >= mod) v0 %= mod;
		return new mlong(v0);
	}
	
	
	public static mlong inv(long x){
		long a = 0, b = 0, c = 0;
		ExtGCD(x, mod, ref a, ref b, ref c);
		return (mlong)((a + mod) % mod);
	}
	
	public static void ExtGCD(long x, long y, ref long a, ref long b, ref long c){
		long r0 = x; long r1 = y;
		long a0 = 1; long a1 = 0;
		long b0 = 0; long b1 = 1;
		long q1, r2, a2, b2;
		while(r1 > 0){
			q1 = r0 / r1;
			r2 = r0 % r1;
			a2 = a0 - q1 * a1;
			b2 = b0 - q1 * b1;
			r0 = r1; r1 = r2;
			a0 = a1; a1 = a2;
			b0 = b1; b1 = b2;
		}
		c = r0;
		a = a0;
		b = b0;
	}
	
	public static mlong ModPow(mlong a, long k){
		if(k == 0) return (mlong) 1;
		if(a == 0) return (mlong) 0;
		mlong x = a;
		mlong ret = 1;
		while(k > 0){
			if(k % 2 == 1) ret *= x;
			x *= x;
			k >>= 1;
		}
		return ret;
	}
	
	
	public static bool operator == (mlong a, mlong b){
		 return a.Equals(b);
	}
	public static bool operator != (mlong a, mlong b){
		 return !(a == b);
	}
	
	public override bool Equals(System.Object obj){
		if(obj  ==  null) return false;
		mlong p  =  (mlong) obj;
		if((System.Object) p  ==  null) return false;
		return p.V  ==  V;
	}
	public override int GetHashCode(){
		return V.GetHashCode();
	}
	
	public static implicit operator mlong(long n){
		long v = n % mod; if(v < 0) v += mod;
		return new mlong(v);
	}
	public static implicit operator mlong(int n){
		long v = n % mod; if(v < 0) v += mod;
		return new mlong(v);
	}
	public static explicit operator long(mlong n){
		return n.V;
	}
	
	public override String ToString(){
		return V.ToString();
	}
	
	
}

Measured memory_bytes: 28348