import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

import numpy as np

N,K = map(int,readline().split())
m = map(int,read().split())
AB = zip(m,m)

MOD = 10 ** 9 + 7

graph = [[] for _ in range(N+1)]
for a,b in AB:
    a+=1; b+=1
    graph[a].append(b)
    graph[b].append(a)

root = 1
parent = [0] * (N+1)
order = []
stack = [root]
while stack:
    x = stack.pop()
    order.append(x)
    for y in graph[x]:
        if y == parent[x]:
            continue
        parent[y] = x
        stack.append(y)

size = [1] * (N+1) # 部分木の大きさ
for v in order[::-1]:
    p = parent[v]
    size[p] += size[v]

def convolve(A,B):
    LA = len(A); LB = len(B)
    if LA > LB:
        A,B = B,A
        LA,LB = LB,LA
    C = np.zeros(LA+LB-1,np.int64)
    for i,x in enumerate(A):
        C[i:i+LB] += A[i] * B % MOD
    C %= MOD
    return C

dp = [np.array([1],np.int64) for _ in range(N+1)]

for v in order[::-1]:
    p = parent[v]
    dp[v] = np.append(dp[v],1)
    dp[p] = convolve(dp[p], dp[v])

answer = dp[root][K]
print(answer)