import java.io.*;
import java.util.*;

public class Main {
    static int[][] dp;
    static int[] children;
    static final int MOD = 1000000007;
    static ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int k = sc.nextInt();
        for (int i = 0; i < n; i++) {
            graph.add(new ArrayList<>());
        }
        for (int i = 0; i < n - 1; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            graph.get(a).add(b);
            graph.get(b).add(a);
        }
        dp = new int[n][n + 1];
        children = new int[n];
        getChildren(0, 0);
        System.out.println(dp[0][k]);
    }
    
    static int getChildren(int idx, int parent) {
        int count = 1;
        dp[idx][0] = 1;
        for (int x : graph.get(idx)) {
            if (x == parent) {
                continue;
            }
            int tmp = getChildren(x, idx);
            for (int i = count - 1; i >= 0; i--) {
                for (int j = 1; j <= children[x]; j++) {
                    dp[idx][i + j] += (int)((long)dp[idx][i] * dp[x][j] % MOD);
                    dp[idx][i + j] %= MOD;
                }
            }
            count += tmp;
        }
        dp[idx][count] = 1;
        return children[idx] = count;
    }
}

class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}