#pragma comment(linker,"/STACK:128000000")
#include <stdio.h>
#include <cstdlib>
#include <cctype>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cassert>

#include <deque>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <utility>
#include <algorithm>
#include <tuple>
#include <iostream>
#include <random>
#include <iterator>
#include <list>
#include <iomanip>
#include <random>
#include <complex>
#include <deque>
#include <numeric>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pii;
typedef pair<double, double> ptd;

const int inf = (int)1e9 + 1000;
const ll infLL = 10000000000000001LL;
const int mod = (int)1e9 + 7;
const double eps = 1e-11;
const double pi = 3.141592653589793;
const int maxlen = (int)2e5 + 10;
const int base = (int)1e9;

const int dd = (int)1001;

#define ACCEPTED return 0;
#define mp make_pair
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define optimize cin.sync_with_stdio(false);cout.sync_with_stdio(false);cin.tie(0);
#define name "bridges"
#define scnaf scanf
#define X first
#define Y second

set<int> g[dd];
set<int> V;
int deg[dd];

ll dfs(int m, int q)
{
    if (m == -1)
        return 0;

    if (V.size() == 1) {
        if (m > 1)
            return 0;
        return m ^ q;
    }

    int u = find(deg + 1, deg + 1 + dd, 1) - deg;

    deg[u] = 0;
    for (int to : g[u]) {
        deg[to]--;
        g[to].erase(u);
    }

    V.erase(u);

    ll ans = 0;
    if (q == 0)
        ans = (dfs(m - 1, 1) + dfs(m, 0)) % mod;
    else
        ans = (dfs(m - 1, 1) + dfs(m, 1)) % mod;

    V.insert(u);
    deg[u] = 1;
    for (int to : g[u]) {
        deg[to]++;
        g[to].insert(u);

    }

    return ans;
}

int main()
{
#ifdef _DEBUG
    freopen("input.txt", "rt", stdin);
    freopen("output.txt", "wt", stdout);
#else
    //    freopen(name".out", "wt", stdout);
//    freopen(name".in", "rt", stdin);
#endif

    int n, m;
    scnaf("%d %d", &n, &m);

    for (int i = 0; i < n - 1; i++) {
        int u, v;
        scnaf("%d %d", &u, &v);

        g[u].insert(v);
        g[v].insert(u);

        V.insert(v);
        V.insert(u);
        deg[u]++;
        deg[v]++;
    }

    ll ans = dfs(m, 0);

    printf("%lld", ans);

    return 0;
}