import io
import sys
import bisect
import math
from itertools import permutations, combinations
from heapq import heappush, heappop
from collections import deque
from collections import defaultdict as dd
sys.setrecursionlimit(10**7+10)

# mod = 998244353
mod = 10**9+7

_INPUT = """\
6 1
0 1
0 2
1 3
2 4
2 5

"""



def main():
    N, K = map(int, input().split())
    G = [[]for _ in range(N)]
    for _ in range(N-1):
        a, b = map(int, input().split())
        G[a].append(b)
        G[b].append(a)
    def dfs(now, par):
        dp = [1] # 黒が0個となる場合の数
        for nxt in G[now]:
            if nxt == par:continue

            ndp = dfs(nxt, now)
            merged = [0]*(len(dp)+len(ndp)-1)

            for i in range(len(dp)):
                for j in range(len(ndp)):
                    merged[i+j] += dp[i]*ndp[j]
                    merged[i+j] %= mod
            dp = merged
        dp.append(dp[-1]) # 自分以外全部黒と、全部黒は同数
        return dp
    
    print(dfs(0, -1)[K])   
                            
if __name__ == "__main__":
    # sys.stdin = io.StringIO(_INPUT)
    main()