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

public class Main {
    static ArrayList<TreeMap<Integer, Long>> dp = new ArrayList<>();
    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++) {
            dp.add(new TreeMap<>());
            dp.get(i).put(0, 1L);
            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);
        }
        getChildren(0, 0);
        System.out.println(dp.get(0).getOrDefault(k, 0L));
    }
    
    static int getChildren(int idx, int parent) {
        int count = 1;
        for (int x : graph.get(idx)) {
            if (x == parent) {
                continue;
            }
            count += getChildren(x, idx);
            Integer key = Integer.MAX_VALUE;
            while ((key = dp.get(idx).lowerKey(key)) != null) {
                long org = dp.get(idx).get(key);
                for (int y : dp.get(x).keySet()) {
                    if (y == 0) {
                        continue;
                    }
                    dp.get(idx).put(key + y, (dp.get(idx).getOrDefault(key + y, 0L) + org * dp.get(x).get(y) % MOD) % MOD);
                }
            }
        }
        dp.get(idx).put(count, 1L);
        return 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();
    }
}