#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;
}