#include <bits/stdc++.h>
int dr[] = {2, 2, -2, -2, 1, -1, 1, -1};
int dc[] = {1, -1, 1, -1, 2, 2, -2, -2};
int dr1[] = {0, 0, 0, 1, 1, 1, -1, -1, -1};
int dc1[] = {-1, 0, 1, -1, 0, 1, -1, 0, 1};
int dr2[] = {0, 0, 1, -1};
int dc2[] = {1, -1, 0, 0};
using namespace std;
long long int cld[100006], sib[100006];
vector<long long int> adj[100006];
void dfs(long long int u, long long int par) {
  sib[u] = 0;
  cld[u] = 0;
  long long int pre = 0;
  long long int i;
  for (i = 0; i < adj[u].size(); i++) {
    long long int p = adj[u][i];
    if (p == par) continue;
    if (pre != 0) sib[pre] = p;
    pre = p;
    if (cld[u] == 0) cld[u] = p;
    dfs(p, u);
  }
}
long long int dp[100006][12][3], k, m;
long long int cal(long long int u, long long int x, long long int f) {
  long long int i;
  if (u == 0) {
    if (x == 0) return 1;
    return 0;
  }
  long long int &r = dp[u][x][f];
  if (r != -1) return r;
  long long int p;
  r = 0;
  if (f == 1) {
    p = k - 1;
    for (i = 0; i <= x; i++) {
      long long int f1 = cal(cld[u], i, 0) * cal(sib[u], x - i, f);
      f1 %= 1000000007;
      r = r + (f1 * p) % 1000000007;
      r %= 1000000007;
    }
    return r;
  }
  if (f == 0) {
    for (i = 0; i < x; i++) {
      long long int f1 = cal(cld[u], i, 1) * cal(sib[u], x - i - 1, f);
      f1 %= 1000000007;
      r = r + f1;
      r %= 1000000007;
    }
  }
  for (i = 0; i <= x; i++) {
    long long int f1 = cal(cld[u], i, 2) * cal(sib[u], x - i, f);
    long long int f2 = cal(cld[u], i, 0) * cal(sib[u], x - i, f);
    f1 %= 1000000007;
    f2 %= 1000000007;
    r = r + (f2 * (k - 1)) % 1000000007;
    r %= 1000000007;
    r = r + (f1 * (m - k)) % 1000000007;
    r %= 1000000007;
  }
  return r;
}
int main() {
  long long int n, i, j, u, v, x;
  cin >> n >> m;
  for (i = 1; i < n; i++) {
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  cin >> k >> x;
  dfs(1, -1);
  memset(dp, -1, sizeof(dp));
  long long int ans = 0;
  for (i = 0; i <= x; i++) {
    ans += cal(1, i, 0);
    ans %= 1000000007;
  }
  cout << ans << endl;
  return 0;
}
