#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;--i)
#define srep(i,s,t) for(int i=(int)(s);i<(int)(t);++i)
#define each(a,b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
#define cmx(x,y) x=max(x,y)
#define cmn(x,y) x=min(x,y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout<<#x<<" = "<<(x)<<endl
#define spair(p) cout<<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout<<" "<<kbrni;cout<<endl
#define smap(m) cout<<#m<<":";each(kbrni,m)cout<<" {"<<kbrni.first<<":"<<kbrni.second<<"}";cout<<endl

using namespace std;

typedef pair<int,int> P;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;

const int MAX_N = 2005;

vector<int> G[MAX_N];
int K;

ll add(ll x,ll y)
{
    return (x + y)%MOD;
}

ll sub(ll x,ll y)
{
    return (x+MOD-y)%MOD;
}

ll mul(ll x,ll y)
{
    return x*y%MOD;
}

vl mul(vl a,vl b)
{
    int n = len(a),m = len(b);
    int sz = n+m-1;
    vl res(sz,0);
    rep(i,n){
        rep(j,m){
            res[i+j] += mul(a[i],b[j]);
        }
    }
    rep(i,sz){
        res[i] %= MOD;
    }
    return res;
}

vl rec(int u,int p)
{
    vl res = {1};
    for(int i=0;i<len(G[u]);i++){
        int v = G[u][i];
        if(v != p){
            res = mul(res,rec(v,u));
        }
    }
    res.pb(1);
    return res;
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n >> K;
    vi a(n),b(n);
    rep(i,n-1){
        int a,b;
        cin >> a >> b;
        G[a].pb(b),G[b].pb(a);
    }
    vl res = rec(0,-1);
    if(len(res) < K){
        cout << "0\n";
    }else{
        cout << res[K] << "\n";
    }
    return 0;
}