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

partial class Solver {
    const int mod = 1000000007;

    int[][] memo = new int[2001][];
    int[] size = new int[2001];

    int[] dfs(List<List<int>> adj, int pos, int parent = -1) {
        int n = adj.Count;
        if (memo[pos] != null)
            return memo[pos];
        int[] ret = new int[n + 1];
        ret[0] = 1;
        size[pos] = 1;
        foreach (var child in adj[pos]) {
            if (child == parent) continue;
            var sub = dfs(adj, child, pos);
            size[pos] += size[child];
            int[] next = new int[n + 1];
            for (int i = 0; i <= size[pos]; i++) {
                if (ret[i] == 0) continue;
                for (int j = 0; j <= size[child]; j++) {
                    next[i + j] += (int)(1L * ret[i] * sub[j] % mod);
                    next[i + j] %= mod;
                }
            }
            ret = next;
        }
        ret[size[pos]] = 1;

        return memo[pos] = ret;
    }

    public void Run() {
        int N = ni();
        int K = ni();
        var adj = Enumerable.Range(0, N).Select(_ => new List<int>()).ToList();

        for (int i = 0; i < N - 1; i++) {
            int a = ni();
            int b = ni();
            adj[a].Add(b);
            adj[b].Add(a);
        }
        var result = dfs(adj, 0);
        cout.WriteLine(result[K]);
    }
}

// PREWRITEN CODE BEGINS FROM HERE
partial class Solver : Scanner {
    public static void Main(string[] args) {
        new Solver(Console.In, Console.Out).Run();
    }

    TextReader cin;
    TextWriter cout;

    public Solver(TextReader reader, TextWriter writer)
        : base(reader) {
        this.cin = reader;
        this.cout = writer;
    }
    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer) {
    }

    public int ni() {
        return NextInt();
    }
    public long nl() {
        return NextLong();
    }
    public string ns() {
        return Next();
    }
}

public class Scanner {
    private TextReader Reader;
    private Queue<String> TokenQueue = new Queue<string>();
    private CultureInfo ci = CultureInfo.InvariantCulture;

    public Scanner()
        : this(Console.In) {
    }

    public Scanner(TextReader reader) {
        this.Reader = reader;
    }

    public int NextInt() { return Int32.Parse(Next(), ci); }
    public long NextLong() { return Int64.Parse(Next(), ci); }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size) {
        var array = new string[size];
        for (int i = 0; i < size; i++) array[i] = Next();
        return array;
    }
    public int[] NextIntArray(int size) {
        var array = new int[size];
        for (int i = 0; i < size; i++) array[i] = NextInt();
        return array;
    }

    public long[] NextLongArray(int size) {
        var array = new long[size];
        for (int i = 0; i < size; i++) array[i] = NextLong();
        return array;
    }

    public String Next() {
        if (TokenQueue.Count == 0) {
            if (!StockTokens()) throw new InvalidOperationException();
        }
        return TokenQueue.Dequeue();
    }

    public bool HasNext() {
        if (TokenQueue.Count > 0)
            return true;
        return StockTokens();
    }

    private bool StockTokens() {
        while (true) {
            var line = Reader.ReadLine();
            if (line == null) return false;
            var tokens = line.Trim().Split(" ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
            if (tokens.Length == 0) continue;
            foreach (var token in tokens)
                TokenQueue.Enqueue(token);
            return true;
        }
    }
}