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

#define repu(i, begin, end) for (__typeof(begin) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
#define repe(i, begin, end) for (__typeof(begin) i = (begin); i != (end) + 1 - 2 * ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
#define mem(a, x) memset(a, x, sizeof(a))
#define all(a) a.begin(), a.end()
#define count_bits(x) __builtin_popcount(x)
#define count_bitsll(x) __builtin_popcountll(x)
#define least_bits(x) __builtin_ffs(x)
#define least_bitsll(x) __builtin_ffsll(x)
#define most_bits(x) 32 - __builtin_clz(x)
#define most_bitsll(x) 64 - __builtin_clz(x)

vector<string> split(const string &s, char c) {
	vector<string> v;
	stringstream ss(s);
	string x;
	while (getline(ss, x, c)) v.push_back(x);
	return v;
}

#define error(args...) { vector<string> _v = split(#args, ','); err(_v.begin(), args); }

void err(vector<string>::iterator it) {}

template<typename T, typename... Args>
void err(vector<string>::iterator it, T a, Args... args) {
	cerr << it -> substr((*it)[0] == ' ', it -> length()) << " = " << a << '\n';
	err(++it, args...);
}

typedef long long ll;
const int MOD = 1000000007;

template<class T> inline T tmin(T a, T b) {return (a < b) ? a : b;}
template<class T> inline T tmax(T a, T b) {return (a > b) ? a : b;}
template<class T> inline void amax(T &a, T b) {if (b > a) a = b;}
template<class T> inline void amin(T &a, T b) {if (b < a) a = b;}
template<class T> inline T tabs(T a) {return (a > 0) ? a : -a;}
template<class T> T gcd(T a, T b) {while (b != 0) {T c = a; a = b; b = c % b;} return a;}

const int N = 2005;
int n, k, t;
int in[N], out[N], sub[N];
ll dp[N + N][N];
vector<int> G[N];

void dfs(int v, int p) {
    in[v] = ++t;
    sub[v] = 1;
    repu(i, 0, G[v].size()) {
        int u = G[v][i];
        if (u != p) {
            dfs(u, v);
            sub[v] += sub[u];
        }
    }
    out[v] = ++t;
}

bool comp(int x, int y) {
    if (out[x] != out[y]) return out[x] < out[y];
    return in[x] > in[y];
}

int main(int argc, char *argv[]) {
    ios_base::sync_with_stdio(false);
    int a, b;

    cin >> n >> k;
    repu(i, 1, n) {
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }
    t = 0;
    dfs(0, -1);
    vector<int> v(n);
    repu(i, 0, n) v[i] = i;
    sort(all(v), comp);

    mem(dp, 0);
    dp[0][0] = 1;
    for (int i = 0, j = 1; i < n && j <= n + n;) {
        repu(l, 0, n + 1) dp[j][l] = dp[j - 1][l];

        if (j == out[v[i]]) {
            repu(l, sub[v[i]], n + 1) {
                dp[j][l] += dp[in[v[i]] - 1][l - sub[v[i]]];
                if (dp[j][l] >= MOD) dp[j][l] -= MOD;
            }
            i++;
        }
        j++;
    }
    
    printf("%lld\n", dp[n + n][k]);

    return 0;
}