#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
vector<int> G[100010];
int k, x, m;
long long dp[100010][20][3], dp2[100010][20][3];
void dfs(int u, int fa) {
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v == fa) continue;
    dfs(v, u);
  }
  dp[u][0][0] = k - 1;
  dp[u][0][1] = m - k;
  dp[u][1][2] = 1;
  for (int i = 0; i < G[u].size(); i++) {
    int v = G[u][i];
    if (v == fa) continue;
    memset(dp2[u], 0, sizeof(dp2[u]));
    for (int j = 0; j <= x; j++) {
      for (int k = 0; k <= x; k++)
        if (j + k <= x) {
          dp2[u][j + k][0] += dp[u][j][0] * dp[v][k][0];
          dp2[u][j + k][0] %= mod;
          dp2[u][j + k][0] += dp[u][j][0] * dp[v][k][1];
          dp2[u][j + k][0] %= mod;
          dp2[u][j + k][0] += dp[u][j][0] * dp[v][k][2];
          dp2[u][j + k][0] %= mod;
          dp2[u][j + k][1] += dp[u][j][1] * dp[v][k][0];
          dp2[u][j + k][1] %= mod;
          dp2[u][j + k][1] += dp[u][j][1] * dp[v][k][1];
          dp2[u][j + k][1] %= mod;
          dp2[u][j + k][2] += dp[u][j][2] * dp[v][k][0];
          dp2[u][j + k][2] %= mod;
        }
    }
    for (int j = 0; j <= x; j++) {
      dp[u][j][0] = dp2[u][j][0];
      dp[u][j][1] = dp2[u][j][1];
      dp[u][j][2] = dp2[u][j][2];
    }
  }
}
int main() {
  int n;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n - 1; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  scanf("%d%d", &k, &x);
  dfs(1, -1);
  long long ans = 0;
  for (int i = 0; i <= x; i++) {
    for (int j = 0; j < 3; j++) {
      ans = (ans + dp[1][i][j]) % mod;
    }
  }
  cout << ans << endl;
  return 0;
}
