import sys

sys.setrecursionlimit(10 ** 9)
MOD = 10 ** 9 + 7

n, k = map(int, input().split())
edges = [[] for _ in range(n)]
for _ in range(n - 1):
    u, v = map(int, input().split())
    edges[u].append(v)
    edges[v].append(u)

def dfs(pos, bpos):
    dp = [1]
    for npos in edges[pos]:
        if npos == bpos:
            continue
        tmp= dfs(npos, pos)
        ndp = [0] * (len(dp)+len(tmp)-1)
        for i, v in enumerate(dp):
            for j, u in enumerate(tmp):
                ndp[i + j] += u * v
                ndp[i + j] %= MOD
        dp = ndp
    dp.append(1)
    return dp

dp= dfs(0, -1)
print(dp[k])