using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Math;

class MainClass : Scanner
{
    static Graph<int> G;
    static int N;
    static int K;
    static bool[] used;
    static void Main()
    {
        (N, K) = ReadTuple<int,int>();
        G = new Graph<int>(N);
        for (int i = 0; i < N-1; i++)
        {
            var r = RInts(_ => int.Parse(_) - 1);
            G.Add(r[0], r[1]);
            G.Add(r[1], r[0]);
        }
        Modular ans = K;
        used = new bool[N];used[0] = true;
        var que = new Queue<int>();
        que.Enqueue(0);
        while (que.Count > 0)
        {
            var now = que.Dequeue();
            int ncnt = G[now].Count;
            
            if (now == 0)
            {
                if (ncnt < 0 || K -1 < ncnt) ans *= 0;
                 else ans *= Modular.Npr(K - 1, ncnt);
            }
            else
            {
                if (K-2 < ncnt-1) ans *= 0;
                else ans *= Modular.Npr(K - 2, ncnt - 1);
            }

            foreach (var next in G[now])
            {
                if (used[next]) continue;

                used[next] = true;
                que.Enqueue(next);
            }
        }
        WriteLine(ans);
    }


    
}
class Modular
{
    private const int M = 1000000007;
    private const int arysize = 2000001;
    private long value;
    public Modular(long value = 0) { this.value = value; }
    public override string ToString() { return value.ToString(); }
    public static implicit operator Modular(long a)
    {
        var m = a % M;
        return new Modular((m < 0) ? m + M : m);
    }
    public static Modular operator +(Modular a, Modular b)
    => a.value + b.value;
    public static Modular operator -(Modular a, Modular b)
    => a.value - b.value;
    public static Modular operator *(Modular a, Modular b)
    => a.value * b.value;
    public static Modular Pow(Modular a, long n)
    {
        Modular ans = 1;
        for (; n > 0; n >>= 1, a *= a)
        {
            if ((n & 1) == 1) ans *= a;
        }
        return ans;
    }
    public static Modular operator /(Modular a, Modular b)
    {
        return a * Pow(b, M - 2);
    }
    private static int[] facs = new int[arysize];
    private static int facscount = -1;

    public static Modular Fac(int n)   //階乗
    {
        facs[0] = 1;
        while (++facscount <= n)
        {
            facs[facscount + 1] = (int)(Math.BigMul(facs[facscount], facscount + 1) % M);
        }
        return facs[n];
    }
    public static Modular Fac(int r, int n)//記録しない階乗
    {
        int temp = 1;
        for (int i = r; i <= n; i++)
        {
            temp = (int)(Math.BigMul(temp, i) % M);
        }
        return temp;
    }
    public static Modular Ncr(int n, int r) //nCr
    {
        return (n < r) ? 0
             : (n == r) ? 1
                        : (Math.Max(n, r) <= arysize) ? Fac(n) / (Fac(r) * Fac(n - r))
                            : Fac(n - r + 1, n) / Fac(r);
    }
    public static Modular Npr(int n,int r)
    {
        r = n - r;
        return Fac(n) / Fac(r);
    }
    public static explicit operator int(Modular a)
    {
        return (int)a.value;
    }
}
class Graph<T>
{
    private List<T>[] G;
    public Graph(int size)
    {
        G = new List<T>[size];
        for (int i = 0; i < size; i++)
        {
            G[i] = new List<T>();
        }
    }

    public List<T> this[int i] => G[i];
    public void Add(int from, T to) => G[from].Add(to);
    public List<T>[] ToListArray() => G;
    public int Length => G.Length;
}


class Scanner
{
    public static string RString() => Console.ReadLine();
    public static int RInt() => ReadTuple<int>();
    public static long RLong() => ReadTuple<long>();
    public static double RDouble() => ReadTuple<double>();

    public static string[] RStrings() => Console.ReadLine().Split();
    public static int[] RInts() => Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
    public static long[] RLongs() => Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
    public static double[] RDoubles() => Array.ConvertAll(Console.ReadLine().Split(), double.Parse);
    public static int[] RInts(Func<string, int> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static long[] RLongs(Func<string, long> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static double[] RDoubles(Func<string, double> func) => Console.ReadLine().Split().Select(func).ToArray();
    //public static string[] RStrings(Func<string, string> func) => Console.ReadLine().Split().Select(func).ToArray();

    public static T1 ReadTuple<T1>()
    {
        var r = RString();
        var r1 = (T1)Convert.ChangeType(r, typeof(T1));
        return r1;
    }
    public static (T1, T2) ReadTuple<T1, T2>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        return (r1, r2);
    }
    public static (T1, T2, T3) ReadTuple<T1, T2, T3>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        var r3 = (T3)Convert.ChangeType(r[2], typeof(T3));
        return (r1, r2, r3);
    }
    public static (T1, T2, T3, T4) ReadTuple<T1, T2, T3, T4>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        var r3 = (T3)Convert.ChangeType(r[2], typeof(T3));
        var r4 = (T4)Convert.ChangeType(r[3], typeof(T4));
        return (r1, r2, r3, r4);
    }
}


Measured memory_bytes: 57512