#include <bits/stdc++.h>
constexpr int MAX_N = 100100;
constexpr int MAX_X = 11;
constexpr int MOD = 1000000007;
using namespace std;
int n, m, k, x;
vector<int> adj[MAX_N];
int memo[MAX_N][MAX_X][3];
void calc(int u, int p) {
  for (int v : adj[u]) {
    if (v == p) continue;
    calc(v, u);
  }
  for (int wrt_k = 0; wrt_k <= 2; wrt_k++) {
    long long tmp[adj[u].size() + 1][x + 1];
    tmp[0][0] = 1;
    for (int i = 1; i <= x; i++) tmp[0][i] = 0;
    int nc = 0;
    for (int i = 0; i < adj[u].size(); i++) {
      if (adj[u][i] == p) continue;
      nc++;
      for (int j = 0; j <= x; j++) {
        tmp[nc][j] = 0;
        for (int j2 = 0; j2 <= j; j2++) {
          long long num_less =
              ((long long)(k - 1) * memo[adj[u][i]][j2][0]) % MOD;
          long long num_equal = memo[adj[u][i]][j2][1];
          long long num_more =
              ((long long)(m - k) * memo[adj[u][i]][j2][2]) % MOD;
          tmp[nc][j] = (tmp[nc][j] + tmp[nc - 1][j - j2] * num_less) % MOD;
          if (wrt_k == 0)
            tmp[nc][j] = (tmp[nc][j] + tmp[nc - 1][j - j2] * num_equal) % MOD;
          if (wrt_k != 1)
            tmp[nc][j] = (tmp[nc][j] + tmp[nc - 1][j - j2] * num_more) % MOD;
        }
      }
    }
    for (int j = ((wrt_k == 1) ? 1 : 0); j <= x; j++) {
      memo[u][j][wrt_k] = tmp[nc][j - (wrt_k == 1)];
    }
  }
}
int main() {
  scanf(" %d %d", &n, &m);
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    scanf(" %d %d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  scanf(" %d %d", &k, &x);
  calc(1, 1);
  int ans = 0;
  for (int i = 0; i <= x; i++) {
    ans = (ans + (long long)(k - 1) * memo[1][i][0]) % MOD;
    ans = (ans + memo[1][i][1]) % MOD;
    ans = (ans + (long long)(m - k) * memo[1][i][2]) % MOD;
  }
  printf("%d\n", ans);
  return 0;
}
