#include<bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("Ofast")
using std::cin;
using std::cout;

using u64 = unsigned long long;
using ll = long long;

struct ds {
	int B, n;
	std::vector<ll> a;
	struct block {
		std::vector<ll> elem;
		ll add;
		void init() { sort(elem.begin(), elem.end()); }
		ll leq(ll x) {
			return upper_bound(elem.begin(), elem.end(), x - add) - elem.begin();
		}
	};
	std::vector<block> v;
	void init(std::vector<ll> s) {
		a = s, n = a.size();
		for(B = 0;3 << (2 * B) < a.size();) ++ B;
		v.resize(((n - 1) >> B) + 1);
		for(int i = 0;i < n;++i) v[i >> B].elem.push_back(a[i]);
		for(block & x : v) x.init();
	}
	void badd(int l, int r, int val) {
		for(int i = l;i <= r;++i) {
			a[i] += val;
		}
		copy(a.begin() + (l >> B << B), a.begin() + std::min((l >> B << B) + (1 << B), n), v[l >> B].elem.begin());
		v[l >> B].init();
	}
	void rangeadd(int l, int r, int val) {
		if((l >> B) == (r >> B)) {
			badd(l, r, val);
			return ;
		}
		badd(l, l | ((1 << B) - 1), val);
		badd(r >> B << B, r, val);
		for(int i = (l >> B) + 1;i < (r >> B);++i) {
			v[i].add += val;
		}
	}
	int qry(int l, int r, ll val) {
		if(val < 0) return 0;
		ll ans = 0;
		for(int i = 0;i < (l >> B);++i) {
			ans += v[i].leq(val);
		}
		for(int i = (r >> B) + 1;i < (int) v.size();++i) {
			ans += v[i].leq(val);
		}
		const ll vL = val - v[l >> B].add;
		const ll vR = val - v[r >> B].add;
		for(int i = (l >> B) << B;i < l;++i) {
			ans += a[i] <= vL;
		}
		for(int i = r + 1, end = std::min((r >> B << B) + (1 << B), n);i < end;++i) {
			ans += a[i] <= vR;
		}
		return ans;
	}
	ll qp(int p) {
		return a[p] + v[p >> B].add;
	}
};
const int N = 200005;
int n, q;
struct edge { int to, nxt; } e[N << 1];
int h[N], num;
void link(int x, int y) {
	e[++num] = {y, h[x]}, h[x] = num;
	e[++num] = {x, h[y]}, h[y] = num;
}
ds d[N];
int vis[N], size[N];
void dfs0(int x, int fa = 0) {
	size[x] = 1;
	for(int i = h[x];i;i = e[i].nxt) if(e[i].to != fa && !vis[e[i].to]) {
		dfs0(e[i].to, x);
		size[x] += size[e[i].to];
	}
}
int mn, root;
void dfs1(int x, int s, int fa = 0) {
	int max = s - size[x];
	for(int i = h[x];i;i = e[i].nxt) if(e[i].to != fa && !vis[e[i].to]) {
		dfs1(e[i].to, s, x);
		max = std::max(max, size[e[i].to]);
	}
	if(max < mn) {
		mn = max;
		root = x;
	}
}
int getroot(int x) {
	dfs0(x), mn = 1e9, dfs1(x, size[x]);
	return root;
}
std::vector<int> elems[N];
int max = 0;
int solve(int x, int d) {
	max = std::max(max, d);
	x = getroot(x), vis[x] = 1;
	elems[d].push_back(x);
	for(int i = h[x];i;i = e[i].nxt) if(!vis[e[i].to]) {
		solve(e[i].to, d + 1);
	}
	return x;
}
int w[N];
int main() {
	std::ios::sync_with_stdio(false), cin.tie(0);
#ifdef zqj
	freopen("$.in", "r", stdin);
#endif
	int n;
	cin >> n;
	for(int i = 1, x, y;i < n;++i) {
		cin >> x >> y;
		link(x, y);
	}
	solve(1, 0);
	cout << max + 1 << '\n';
	for(int i = max;i >= 0;--i) {
		cout << elems[i].size();
		for(int x : elems[i]) cout << ' ' << x;
		cout << '\n';
	}
}