import sys
sys.setrecursionlimit(2100)
import numpy as n
N,K=map(int,input().split())
c=[[] for _ in range(N)]
s=[0]*N
for i in range(N-1):
	a,b=map(int,input().split())
	c[a].append(b)
	c[b].append(a)
def f(x):
	v=n.array([1],dtype="O")
	s[x]=1
	for i in c[x]:
		if s[i]:continue
		v=n.convolve(v,f(i))%int(1e9+7)
	return n.append(v,1)

print(f(0)[K])