// what is matter? never mind. 
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,sse4,popcnt,abm,mmx,avx,avx2")
#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rep(i,a,b) for(int i=(a);i>=(b);--i)
#define ll long long
//#define ull unsigned long long
//#define int long long
#define SZ(x) ((int)((x).size()))
#define ALL(x) (x).begin(),(x).end()
using namespace std;
inline int read()
{
	char c=getchar();int x=0;bool f=0;
	for(;!isdigit(c);c=getchar())f^=!(c^45);
	for(;isdigit(c);c=getchar())x=(x<<1)+(x<<3)+(c^48);
	return f?-x:x;
}

#define fi first
#define se second
#define pb push_back
#define mkp make_pair
typedef pair<int,int>pii;
typedef vector<int>vi;

#define maxn 500005
#define inf 0x3f3f3f3f

int n;
vi e[maxn];
vector<vi>out;

vi que;
void dfs(int u,int pa){
	que.pb(u);
	for(int v:e[u]) if(v!=pa) dfs(v,u);
}

void work()
{
	n=read();
	For(i,1,n) e[i].clear(); out.clear();
	For(i,2,n){
		int u=read(),v=read();
		e[u].pb(v),e[v].pb(u);
	}
	
	For(i,1,n) if(e[i].size()==1){
		que.clear();
		dfs(i,0);
		reverse(ALL(que));
		out.pb(que);
	}
	
	cout<<SZ(out)<<"\n";
	for(auto it:out){
		for(int x:it)cout<<x<<" ";
		cout<<"\n";
	}
}

signed main()
{
	int T=read();
	while(T--)work();
    return 0;
}
/*

*/