import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

MOD = 10**9 + 7

N, K = map(int, readline().split())
m = map(int, read().split())
graph = [[] for _ in range(N + 1)]
for a, b in zip(m, m):
    graph[a].append(b)
    graph[b].append(a)

root = 1
parent = [0] * (N + 1)
order = []
stack = [root]
while stack:
    x = stack.pop()
    order.append(x)
    for y in graph[x]:
        graph[y].remove(x)
        parent[y] = x
        stack.append(y)

dp1 = [None] * (N + 1)
dp2 = [None] * (N + 1)

def compute_at(v):
    n = len(graph[v])
    A = np.ones(K + 1, np.int64)
    A[0] = 0
    B = np.zeros(K + 1, np.int64)
    for w in graph[v]:
        x = dp1[w][::-1].cumsum()[::-1] % MOD
        y = dp2[w].cumsum()
        y[1:] += dp1[w][:-1].cumsum()
        y %= MOD
        B = (B * x + A * y) % MOD
        A = (A * x) % MOD
    dp1[v] = A
    dp2[v] = B

for v in order[::-1]:
    compute_at(v)

x = (dp1[root] + dp2[root]).sum()
print(x % MOD)