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

public class Main {
    static ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
    static long[][] ans;
    static int[] counts;
    static final int MOD = 1000000007;
    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);
        }
        counts = new int[n];
        ans = new long[n][n + 1];
        getCount(0, 0);
        System.out.println(ans[0][k]);
    }
    
    static void getCount(int idx, int p) {
        ans[idx][0] = 1;
        for (int x : graph.get(idx)) {
            if (x == p) {
                continue;
            }
            getCount(x, idx);
            for (int i = counts[idx]; i >= 0; i--) {
                for (int j = counts[x]; j >= 1; j--) {
                    ans[idx][i + j] += ans[idx][i] * ans[x][j] % MOD;
                    ans[idx][i + j] %= MOD;
                }
            }
            counts[idx] += counts[x];
        }
        counts[idx]++;
        ans[idx][counts[idx]] = 1;
    }
} 
class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}