def read_data():
    N, K = map(int, input().split())
    Es = [[] for i in range(N)]
    for i in range(N - 1):
        a, b = map(int, input().split())
        Es[a].append(b)
        Es[b].append(a)
    return N, K, Es


def solve(N, K, Es):
    if K == 0:
        return 1
    if N == K:
        return 1
    root = 0
    parent = -1
    lst = f(root, parent, Es)
    lst.append(1)
    return lst[K]


def f(node, parent, Es):
    if len(Es[node]) == 1:
        return [1, 1]
    lst = [1]
    for child in Es[node]:
        if child == parent:
            continue
        lst_c = f(child, node, Es)
        lst = merge(lst, lst_c)
    lst.append(1)
    return lst


def merge(lst1, lst2):
    mod = 10**9 + 7
    lst = [0] * (len(lst1) + len(lst2) - 1)
    for i, vi in enumerate(lst1):
        for j, vj in enumerate(lst2):
            lst[i + j] += vi * vj
    return [v % mod for v in lst]


N, K, Es = read_data()
print(solve(N, K, Es))