#include<bits/stdc++.h>
#define ll long long
#define vi vector<int>
#define vll vector<ll>
#define eb emplace_back
#define pb push_back
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define sz(v) ((int)v.size())
#define pii pair<int,int>
#define pll pair<ll,ll>
#define fi first
#define se second
#define umap unordered_map
#define uset unordered_set
#define mset multiset
#define i128 __int128
using namespace std;
namespace qiqi {
	void main() {
		int n;
		cin >> n;
		vector<vi> e(n);
		for (int i = 0; i < n-1; i++) {
			int u,v;
			cin >> u >> v; u--; v--;
			e[u].eb(v); e[v].eb(u);
		}
		vi dep(n);
		{
			vi vis(n),siz(n),mx(n);
			auto solve = [&](auto self,int u,int d) -> void {
				vi vec;
				auto dfs = [&](auto self,int u,int fa) -> void {
					vec.eb(u); siz[u] = 1; mx[u] = 0;
					for (auto v:e[u]) {
						if (v != fa && !vis[v]) {
							self(self,v,u);
							siz[u] += siz[v];
							mx[u] = max(mx[u],siz[v]);
						}
					}
				};
				dfs(dfs,u,-1);
				int sum = siz[u];
				u = *min_element(all(vec),[&](int i,int j) {
					return max(mx[i],sum-siz[i]) < max(mx[j],sum-siz[j]);
				});
				vis[u] = 1; dep[u] = d;
				for (auto v:e[u]) {
					if (!vis[v]) {
						self(self,v,d+1);
					}
				}
			};
			solve(solve,0,0);
		}
		int m = *max_element(all(dep))+1;
		vector<vi> vec(m);
		for (int i = 0; i < n; i++) {
			vec[dep[i]].eb(i);
		}
		reverse(all(vec));
		cout << m << '\n';
		for (auto p:vec) {
			cout << sz(p) << ' ';
			for (auto x:p) {
				cout << x+1 << ' ';
			}
			cout << '\n';
		}
	}
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	qiqi::main();
	return 0;
}