#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }


int N;
vector<int> A, B;

vector<int> ds;

vector<vector<int>> G;
vector<int> sz, del;
void dfsSz(int u, int p) {
  sz[u] = 1;
  for (const int i : G[u]) {
    const int v = A[i] ^ B[i] ^ u;
    if (v != p) {
      dfsSz(v, u);
      sz[u] += sz[v];
    }
  }
}
string dfsString(int u, int p) {
  ostringstream oss;
  oss << "[" << u;
  for (const int i : G[u]) {
    const int v = A[i] ^ B[i] ^ u;
    if (!del[v] && v != p) {
      oss << " " << dfsString(v, u);
    }
  }
  oss << "]";
  return oss.str();
}
/// vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
void dfs(int j, int u, int p, int d) {
  for (const int i : G[u]) {
    const int v = A[i] ^ B[i] ^ u;
    if (!del[v] && v != p) {
      dfs(j, v, u, d + 1);
    }
  }
}
/// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
void solveSubtree(int depth, int r) {
#ifdef LOCAL
  cerr << string(2 * depth, ' ') << "solveSubtree " << dfsString(r, -1) << endl;
#endif
  vector<int> is, vs;
  for (const int i : G[r]) {
    const int v = A[i] ^ B[i] ^ r;
    if (!del[v]) {
      is.push_back(i);
      vs.push_back(v);
    }
  }
  const int len = vs.size();
  /// vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
  ds[r] = depth;
  /*
  for (int j = 0; j < len; ++j) {
    const int i = is[j], v = vs[j];
    dfs(j, v, r, 1);
  }
  */
  /// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
}
void solveRec(int depth, int u) {
  for (; ; ) {
    int vm = -1;
    for (const int i : G[u]) {
      const int v = A[i] ^ B[i] ^ u;
      if (!del[v]) {
        if (!~vm || sz[vm] < sz[v]) {
          vm = v;
        }
      }
    }
    if (!~vm || 2 * sz[vm] <= sz[u]) {
      solveSubtree(depth, u);
      del[u] = 1;
      for (const int i : G[u]) {
        const int v = A[i] ^ B[i] ^ u;
        if (!del[v]) {
          solveRec(depth + 1, v);
        }
      }
      break;
    } else {
      sz[u] -= sz[vm];
      sz[vm] += sz[u];
      u = vm;
    }
  }
}
void centroidDecomp() {
  sz.assign(N, 0);
  dfsSz(0, -1);
  del.assign(N, 0);
  solveRec(0, 0);
}


int main() {
  for (; ~scanf("%d", &N); ) {
    A.resize(N - 1);
    B.resize(N - 1);
    for (int i = 0; i < N - 1; ++i) {
      scanf("%d%d", &A[i], &B[i]);
      --A[i];
      --B[i];
    }
    
    G.assign(N, {});
    for (int i = 0; i < N - 1; ++i) {
      G[A[i]].push_back(i);
      G[B[i]].push_back(i);
    }
    ds.assign(N, -1);
    centroidDecomp();
// cerr<<"ds = "<<ds<<endl;
    
    int len = 0;
    for (int u = 0; u < N; ++u) {
      chmax(len, ds[u]);
    }
    ++len;
    
    vector<vector<int>> uss(len);
    for (int u = 0; u < N; ++u) {
      uss[ds[u]].push_back(u);
    }
    
    printf("%d\n", len);
    for (int d = len; --d >= 0; ) {
      printf("%d", (int)uss[d].size());
      for (const int u : uss[d]) {
        printf(" %d", u + 1);
      }
      puts("");
    }
  }
  return 0;
}