#include <bits/stdc++.h>
using namespace std;
template <typename TH>
void _dbg(const char* sdbg, TH h) {
  cerr << sdbg << "=" << h << "\n";
}
template <typename TH, typename... TA>
void _dbg(const char* sdbg, TH h, TA... t) {
  while (*sdbg != ',') cerr << *sdbg++;
  cerr << "=" << h << ",";
  _dbg(sdbg + 1, t...);
}
template <class C>
void mini(C& a4, C b4) {
  a4 = min(a4, b4);
}
template <class C>
void maxi(C& a4, C b4) {
  a4 = max(a4, b4);
}
template <class T1, class T2>
ostream& operator<<(ostream& out, pair<T1, T2> pair) {
  return out << "(" << pair.first << ", " << pair.second << ")";
}
template <class A, class B, class C>
struct Triple {
  A first;
  B second;
  C third;
  bool operator<(const Triple& t) const {
    if (first != t.first) return first < t.first;
    if (second != t.second) return second < t.second;
    return third < t.third;
  }
};
template <class T>
void ResizeVec(T&, vector<long long>) {}
template <class T>
void ResizeVec(vector<T>& vec, vector<long long> sz) {
  vec.resize(sz[0]);
  sz.erase(sz.begin());
  if (sz.empty()) {
    return;
  }
  for (T& v : vec) {
    ResizeVec(v, sz);
  }
}
template <class A, class B, class C>
ostream& operator<<(ostream& out, Triple<A, B, C> t) {
  return out << "(" << t.first << ", " << t.second << ", " << t.third << ")";
}
template <class T>
ostream& operator<<(ostream& out, vector<T> vec) {
  out << "(";
  for (auto& v : vec) out << v << ", ";
  return out << ")";
}
const long long P = 1e9 + 7;
const long long N = 1e5 + 5;
const long long X = 12;
long long dp[N][X][3];
long long n, m, k, x;
long long vis[N];
vector<long long> slo[N];
vector<vector<long long> > trans = {{0, 0, 1}, {1, 1, 1}, {2, 2, 2}};
vector<vector<long long> > mult;
long long ndp[X][3];
void Dfs(long long v) {
  vis[v] = 1;
  dp[v][1][2] = 1;
  dp[v][0][0] = 1;
  for (auto nei : slo[v]) {
    if (vis[nei]) {
      continue;
    }
    Dfs(nei);
    for (long long i = 0; i < (X); ++i) {
      for (long long j = 0; j < (3); ++j) {
        ndp[i][j] = 0;
      }
    }
    for (long long me = (0); me <= (x); ++me) {
      for (long long him = (0); him <= (x - me); ++him) {
        for (long long t1 = 0; t1 < (3); ++t1) {
          for (long long t2 = 0; t2 < (3); ++t2) {
            long long nt = trans[t1][t2];
            long long ns = me + him;
            ndp[ns][nt] = (ndp[ns][nt] + dp[v][me][t1] * dp[nei][him][t2] % P *
                                             mult[t1][t2]) %
                          P;
          }
        }
      }
    }
    for (long long i = 0; i < (X); ++i) {
      for (long long j = 0; j < (3); ++j) {
        dp[v][i][j] = ndp[i][j];
      }
    }
  }
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(10);
  if (0) cout << fixed << setprecision(10);
  cin.tie(0);
  cin >> n >> m;
  for (long long i = (1); i <= (n - 1); ++i) {
    long long a, b;
    cin >> a >> b;
    slo[a].push_back(b);
    slo[b].push_back(a);
  }
  cin >> k >> x;
  mult = {{m - 1, k - 1, 1}, {m - 1, k - 1, 1}, {k - 1, k - 1, 0}};
  Dfs(1);
  long long res = 0;
  vector<long long> hehs = {m - 1, k - 1, 1};
  for (long long i = (0); i <= (x); ++i) {
    for (long long tr = 0; tr < (3); ++tr) {
      res = (res + dp[1][i][tr] * hehs[tr]) % P;
      if (0) cout << dp[1][i][tr] << " ";
    }
    if (0) cout << endl;
  }
  cout << res << endl;
  return 0;
}
