#ifdef LOGX
#define _GLIBCXX_DEBUG
#endif
#include <bits/extc++.h>
using namespace std;
#include <atcoder/modint>
#include <atcoder/convolution>
//using namespace atcoder;

/*---------macro---------*/
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = s; i < (int)(n); i++)
#define ALL(a) a.begin(),a.end()
#define RALL(a) a.rbegin(),a.rend()
#define mybit(i,j) (((i)>>(j))&1)

/*---------type/const---------*/
typedef long long ll;
typedef unsigned long long ull;
typedef std::string::const_iterator state; //構文解析
const int big=1000000007;
//const int big=998244353;
const double EPS=1e-8; //適宜変える
const int dx[4]={1,0,-1,0};
const int dy[4]={0,1,0,-1};
const char newl='\n';
struct{
    constexpr operator int(){return -int(1e9)-10;}
    constexpr operator ll(){return -ll(1e18)-10;}
}neginf;
struct{
    constexpr operator int(){return int(1e9)+10;}
    constexpr operator ll(){return ll(1e18)+10;}
    constexpr auto operator -(){return neginf;}
}inf;

/*---------debug---------*/
#ifdef LOGX
#include <template/debug.hpp>
#else
#define dbg(...) ;
#define dbgnewl ;
#define prt(x) ;
#define _prt(x) ;
#endif

/*---------function---------*/
template<typename T> T max(const std::vector<T> &a){T ans=a[0];for(T elem:a){ans=max(ans,elem);}return ans;}
template<typename T> T min(const std::vector<T> &a){T ans=a[0];for(T elem:a){ans=min(ans,elem);}return ans;}
template<typename T,typename U> bool chmin(T &a,const U b){if(a>b){a=b;return true;}return false;}
template<typename T,typename U> bool chmax(T &a,const U b){if(a<b){a=b;return true;}return false;}
bool valid(int i,int j,int h,int w){return (i>=0 && j>=0 && i<h && j<w);}
template<class T,class U>T expm(T x,U y,const ll mod=big){T res=1;while(y){if(y&1)(res*=x)%=mod;(x*=x)%=mod;y>>=1;}return res;}
template<class T,class U>T exp(T x,U y){T res=1;while(y){if(y&1)res*=x;x*=x;y>>=1;}return res;}

using mint=atcoder::modint1000000007;

int main(){
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cout.precision(10);
/*------------------------------------*/
    
    int n,k;cin >> n >> k;
    vector<vector<int>> tree(n);
    rep(i,n-1){
        int a,b;cin >> a >> b;
        tree[a].emplace_back(b);
        tree[b].emplace_back(a);
    }
    vector white(n,vector<mint>(k+1,0));
    vector<int> sz(n);
    auto dfs=[&](auto &Self,int v,int p=-1)->int{
        int now_sz=1;
        //その頂点を白にする.
        vector<vector<mint>> cnt;
        for(auto ne:tree[v]){
            if(ne==p)continue;
            now_sz+=Self(Self,ne,v);
            cnt.emplace_back(white[ne]);
            if(sz[ne]<=k){
                cnt[(int)cnt.size()-1][sz[ne]]+=1;
            }
        }
        vector<mint> now={1};
        rep(i,cnt.size()){
            now=atcoder::convolution<mint>(now,cnt[i]);
            now.resize(k+1);
        }
        now.resize(k+1);
        white[v]=now;
        return sz[v]=now_sz;
    };
    dfs(dfs,0);
    cout << (white[0][k]+(sz[0]==k)).val() << newl;;
}