N,K = map(int,input().split())
G = [[] for _ in range(N)]
for _ in range(N-1):
    u,v = map(int,input().split())
    G[u].append(v)
    G[v].append(u)

visited = [0]*N
size = [0]*N
dp = [[] for _ in range(N)] #dp[v][k]:vの部分木でk個黒が塗られている数

MOD = 10**9+7
def dfs(cur):
    visited[cur] = 1
    size[cur] = 1
    dp_cur = [1]
    for nxt in G[cur]:
        if visited[nxt]:
            continue
        dfs(nxt)
        dp_nxt = dp[nxt]
        ndp = [0]*(size[cur]+size[nxt]-1)
        for i in range(size[cur]):
            for j in range(size[nxt]):
                ndp[i+j] += dp_cur[i]*dp_nxt[j]
                ndp[i+j] %= MOD
        dp_cur = ndp
        size[cur] += (size[nxt]-1)
    dp_cur.append(1)
    size[cur] += 1
    dp[cur] = dp_cur

dfs(0)
print(dp[0][K])
#print(dp)