n,k=map(int,input().split())
edge=[[] for i in range(n)]
for i in range(n-1):
  a,b=map(int,input().split())
  edge[a].append(b)
  edge[b].append(a)

mod=10**9+7
dp=[[0]*(n+1) for i in range(n)]
for i in range(n):
  dp[i][0]=1
  if len(edge[i])==1 and i!=0:
    dp[i][1]=1
d=[(0,0,0)]
seen=[1]*n
size=[1]*n
while d:
  x,y,z=d.pop()
  if x==0:
    seen[y]=0
    for i in edge[y]:
      if seen[i]:
        d.append((1,i,y))
        d.append((0,i,y))
  else:
    dp_new=[0]*(n+1)
    for k1 in range(size[z]):
      for k2 in range(size[y]+1):
        dp_new[k1+k2]+=dp[z][k1]*dp[y][k2]
    size[z]+=size[y]
    for i in range(size[z]+1):
      dp[z][i]=dp_new[i]%mod
    dp[z][size[z]]=1

print(dp[0][k])