#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;

#define fi first
#define se second
#define repl(i,a,b) for(ll i=(ll)(a);i<(ll)(b);i++)
#define rep(i,n) repl(i,0,n)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define mmax(x,y) (x>y?x:y)
#define mmin(x,y) (x<y?x:y)
#define maxch(x,y) x=mmax(x,y)
#define minch(x,y) x=mmin(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt __builtin_popcountll

#define INF 1e16
#define mod 1000000007

ll N,K;
ll cnt[5001];
ll dp[5001][5001];
ll dp2[2][5001];
vector<int> g[5001];

void dfs(int v,int pre){
  cnt[v]=1;
  for(int nv : g[v]){
    if(nv==pre)continue;
    dfs(nv,v);
    cnt[v]+=cnt[nv];
  }
  int crt=0,nxt=1;
  rep(j,cnt[v]+1)dp2[crt][j]=0;
  dp2[crt][0]=1;
  for(int nv : g[v]){
    if(nv==pre)continue;
    rep(j,cnt[v]+1)dp2[nxt][j]=0;
    rep(j,cnt[v]+1){
      if(dp2[crt][j]==0)break;
      rep(k,cnt[nv]+1){
        if(j+k<cnt[v])(dp2[nxt][j+k]+=dp2[crt][j]*dp[nv][k]%mod)%=mod;
        else break;
      }
    }
    swap(crt,nxt);
  }
  rep(j,cnt[v]){
    dp[v][j]=dp2[crt][j];
  }
  dp[v][cnt[v]]=1;
}

int main(){
  scanf("%lld%lld",&N,&K);
  rep(i,N-1){
    int a,b;
    scanf("%d%d",&a,&b);
    g[a].push_back(b); g[b].push_back(a);
  }
  dfs(0,-1);
  cout<<dp[0][K]<<endl;
  return 0;
}