import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)
mod = 10 ** 9 + 7

N, K = map(int, input().split())
edge = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    edge[a].append(b)
    edge[b].append(a)

# topoligical sort
par = [-1] * N
topo = []
que = [0]
while que:
    s = que.pop()
    topo.append(s)
    for t in edge[s]:
        if t == par[s]:
            continue
        par[t] = s
        que.append(t)


dp = [-1] * N  # dp[v][i], vが根の部分木で黒で塗るノードがi個の数
sz = [0] * N
for s in topo[::-1]:
    sz[s] = 1
    dp[s] = [0] * 2
    dp[s][0] = 1
    for t in edge[s]:
        if t == par[s]:
            continue
        merge = [0] * (sz[s] + sz[t] + 1)
        for i, x in enumerate(dp[s]):
            for j, y in enumerate(dp[t]):
                merge[i+j] += x * y
                merge[i+j] %= mod
        sz[s] += sz[t]
        dp[s] = merge
    dp[s][sz[s]] = dp[s][sz[s] - 1]

print(dp[0][K])