#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll N=3e5+7,mod=998244353;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
#define fi first
#define se second
#define all(x) (x).begin(),(x).end()
vector<ll>e[N];
vector<pll>ans;
ll dep[N];
ll root;
bool f;
ll dfs(ll now,ll fa){
    dep[now]=dep[fa]+1;
    vector<pll>ve;
    for(auto it:e[now]){
        if(it==fa)continue;
        ll x=dfs(it,now);
        ve.emplace_back(dep[x],x);
    }
    if(now==root){
        sort(all(ve));
        for(int i=0;i+1<ve.size();i+=2){
            ans.emplace_back(ve[i].se,ve[i+1].se);
        }
        if(ve.size()&1){
            ll leaf=ve.back().se;
            if(dep[leaf]-dep[root]>=2){
                ans.emplace_back(leaf,root);
            }else f=0;
        }
        return 0;
    }
    if(e[now].size()==1)return now;
    else if(e[now].size()==2)return ve[0].se;
    sort(all(ve));
    for(int i=0;i+1<ve.size();i+=2){
        ans.emplace_back(ve[i].se,ve[i+1].se);
    }
    if(ve.size()&1){
        return ve.back().se;
    }else{
        return now;
    }
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    int tt;
    cin>>tt;
    while(tt--){
        ll n;cin>>n;
        for(int i=1;i<=n;i++)e[i].clear();
        ans.clear();
        root=1;f=1;
        for(int i=0;i<n-1;i++){
            ll x,y;cin>>x>>y;
            e[x].emplace_back(y),e[y].emplace_back(x);
        }
        for(int i=1;i<=n;i++)if(e[i].size()&1==0){root=i;break;}
        dep[root]=0;
        dfs(root,root);
        if(f){
            cout<<ans.size()<<'\n';
            for(auto [it1,it2]:ans)cout<<it1<<' '<<it2<<'\n';
        }else cout<<"-1\n";


    }
}