#include <iostream> #include <algorithm> #include <vector> using namespace std; typedef long long ll; #define M 1000000007 int n,k,s[2005]; vector<int>g[100005]; ll dp[2005][2005]; void dfs(int v,int p){ s[v]=1; dp[v][0]=1; for(int i=0;i<g[v].size();i++){ int u=g[v][i]; if(u!=p){ dfs(u,v); ll r[2005]={}; for(int i=0;i<s[v];i++){ for(int j=0;j<=s[u];j++){ r[i+j]=(r[i+j]+dp[v][i]*dp[u][j]%M)%M; } } for(int i=0;i<=k;i++)dp[v][i]=r[i]; s[v]+=s[u]; } } dp[v][s[v]]=1; } int main(void){ cin>>n>>k; for(int i=0;i<n-1;i++){ int a,b; cin>>a>>b; g[a].push_back(b); g[b].push_back(a); } dfs(0,-1); cout<<dp[0][k]<<endl; }