#include<bits/stdc++.h>
using namespace std;
#define int long long
#define INF 0x3f3f3f3f3f3f3f3f
#define pii pair<int,int>
#define fi first
#define se second
#define all(_a) _a.begin(), _a.end()
const int N=300010;
vector<int> g[N];
int dep[N];
int d[N];

vector<pii>res;
bool cmp(int a,int b){
    return dep[a]<dep[b];
}
bool cmpf(int a,int b){
    return dep[a]>dep[b];
}
vector<int> dfs(int u,int fa){
    //cout<<fa<<"->"<<u<<endl;
    vector<int>add;
    for(auto v:g[u]){
        if(v==fa)continue;
        auto ad=dfs(v,u);
        for(auto v:ad){
            add.push_back(v);
        }   
    }       
    while(add.size()>=2){
        int u=add.back();
        add.pop_back();

        int v=add.back();
        add.pop_back();
        res.push_back({u,v});
    }
    if(add.size()==0)add.push_back(u);
   
    return add;
}
void solve(){
    int n;
    cin>>n;
    res.clear();
    for(int i=1;i<=n;i++){
        g[i].clear();
        d[i]=0;
    }
    for(int i=1;i<n;i++){
        int x,y;
        cin>>x>>y;
        d[x]++;
        d[y]++;
        g[x].push_back(y);
        g[y].push_back(x);
    }
 
    int pos=0;
    for(int i=1;i<=n;i++){
        if(d[i]%2==0){
            pos=i;
            break;
        }
    }
    //cout<<pos<<endl;
    if(pos==0){
        cout<<-1<<endl;
        return ;
    }
    dfs(pos,0);
   
    cout<<res.size()<<endl;
    for(auto v:res){
        cout<<v.fi<<" "<<v.se<<endl;
    }
}
signed main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr), cout.tie(nullptr);
    cout << setiosflags(ios::fixed) << setprecision(15);
    int T;
    T=1;
    cin>>T;
    while(T--)solve();
    return 0;
}