import sys
input = sys.stdin.readline
sys.setrecursionlimit(2010)

def dfs(v, pv):
    dp = [1]
    
    for nv in G[v]:
        if nv==pv:
            continue
        
        ndp = dfs(nv, v)
        merge = [0]*(len(dp)+len(ndp)-1)
        
        for i in range(len(dp)):
            for j in range(len(ndp)):
                merge[i+j] = (merge[i+j]+dp[i]*ndp[j])%MOD
        
        dp = merge
        
    dp.append(dp[-1])
    return dp

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)

MOD = 10**9+7
print(dfs(0, -1)[K])