//#pragma GCC optimize("O3")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("avx,avx2,bmi,bmi2,popcnt,lzcnt")
#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(x) x.begin(), x.end()

mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

int32_t main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    int n;
    cin >> n;
    vector<vector<bool>> adj(n, vector<bool>(n));
    for (int i = 0; i < n - 1; ++i) {
        int u, v;
        cin >> u >> v;
        --u, --v;
        adj[u][v] = adj[v][u] = 1;
    }
    vector<vector<int>> ans;
    vector<int> del(n);
    for (int i = 0; i < 10; ++i) {
        int prev = 0;
        for (int j = 0; j < n; ++j) prev += del[j] == 0;
        ans.push_back({});
        vector<int> c0, c1;
        vector<int> col(n, 0);
        auto dfs = [&](auto dfs, int u, int p) -> void {
            if (del[u] == 0) {
                if (col[u] == 0) c0.push_back(u);
                else c1.push_back(u);
            }
            for (int to = 0; to < n; ++to) {
                if (adj[u][to] && to != p) {
                    col[to] = col[u] ^ (1 ^ del[to]);
                    dfs(dfs, to, u);
                }
            }
        };
        dfs(dfs, rnd() % n, -1);
        if (c0.size() < c1.size()) swap(c0, c1);
        for (auto j : c0) {
            for (auto k : c0) {
                assert(adj[j][k] == 0);
            }
        }
        for (auto j : c0) {
            ans.back().push_back(j);
            del[j] = 1;
        }
        int now = 0;
        for (int j = 0; j < n; ++j) now += del[j] == 0;
        assert(now * 2 <= prev);
    }
    while (ans.back().empty()) ans.pop_back();
    cout << ans.size() << '\n';
    for (auto i : ans) {
        cout << i.size();
        for (auto j : i) cout << ' ' << j + 1;
        cout << '\n';
    }
}