#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <assert.h>

using namespace std;

typedef long long ll;

#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(ll i=(a);i<(b);++i)
#define per(i,a,b) for(ll i=b-1LL;i>=(a);--i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
#define ctos(c) string(1,c)
#define endl "\n"
#define print(x) cout<<#x<<" = "<<x<<endl;

#define MOD 1000000007

ll dp1[1010][1010];
ll dp2[1010][1010];
ll dp3[1010][1010];

long long modpow(long long a, long long b){ 
  long long r = 1LL;
  while(b){
    if(b & 1LL)r *= a;
    if(r >= MOD)r %= MOD;
    a *= a;
    if(a >= MOD)a %= MOD;
    b >>= 1LL;
  }
  return r%MOD;
}

vector<vector<ll> > vv;

void dfs1(ll a, ll p){
  rep(i,1,1005){
    ll b = 1;
    rep(j,0,vv[a].sz){
      if(vv[a][j]==p)continue;
      if(i==1)dfs1(vv[a][j],a);
      b *= dp1[vv[a][j]][i];
      b %= MOD;
    }
    dp1[a][i] = dp1[a][i-1]+b;
    dp1[a][i] %= MOD;
  }
}

void dfs2(ll a, ll p){
  ll e = 0;
  rep(i,1,1005){
    if(p==-1){
      dp2[a][i] = dp1[a][i];
      dp3[a][i] = MOD+dp1[a][i]-dp1[a][i-1];
      dp3[a][i] %= MOD;
    }
    else{
      dp3[a][i] = e*(MOD+dp1[a][i]-dp1[a][i-1]);
      dp3[a][i] %= MOD;
      ll b = (MOD+dp2[p][i]-dp2[p][i-1])%MOD;
      b *= modpow(dp1[a][i],MOD-2);
      b %= MOD;
      b += e;
      b %= MOD;
      e = b;
      dp2[a][i] = b*(MOD+dp1[a][i]-dp1[a][i-1]);
      dp2[a][i] += dp2[a][i-1];
      dp2[a][i] %= MOD;
    }
  }
  rep(j,0,vv[a].sz){
    if(vv[a][j]==p)continue;
    dfs2(vv[a][j],a);
  }
}

int main(){
  ll n,k;
  cin>>n>>k;
  vector<vector<ll> > vv_(n,vector<ll>());
  vv = vv_; 
  rep(i,0,n-1){
    ll a,b;
    cin>>a>>b;
    a--;b--;
    vv[a].pb(b);
    vv[b].pb(a);
  }
  clr(dp1,0);
  clr(dp2,0);
  clr(dp3,0);
  dfs1(0,-1);
  dfs2(0,-1);
  ll ans = 0;
  rep(i,0,n){
    rep(j,1,k+1){
      ans += dp3[i][j];
      ans %= MOD;
    }
  }
  cout << ans << endl;
  return 0;
}