#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef array<int,2> pr;
const int N = 3e5+10;
int T,n,p[N],deg[N];
vector<int> e[N];

set<pr> S;
void output(){
    cout<<S.size()<<"\n";
    for(auto [x,y] : S)cout<<x<<" "<<y<<"\n";
}

void mdf(int x,int y,int v){
    if(x>y)swap(x,y);
    if(v==1)S.insert((pr){x,y}),p[x] = y,p[y] = x;
    else S.erase((pr){x,y});
}
int dfs(int u,int fa){
    int res = 0;
    for(auto v : e[u])if(v != fa){
        int w = dfs(v,u);
        if(w)mdf(w,u,1);
        else{
            if(res)mdf(res,v,1),res = 0;
            else res = v;
        }
    }
    return res;
}

void solve(){
    cin>>n; S.clear();
    for(int i=1;i<=n;i++)e[i].clear(),deg[i] = 0,p[i] = 0;
    for(int i=1,u,v;i<n;i++){
        cin>>u>>v;
        e[u].push_back(v); e[v].push_back(u);
        deg[u]++; deg[v]++;
    }
    if(n&1){
        dfs(1,0);
        return output();
    }else{
        for(int u=1;u<=n;u++)if(deg[u]%2==0){
            int v = e[u][0];
            int x = dfs(u,v),y = dfs(v,u);
            if(x && y)mdf(x,y,1);
            else if(x)mdf(x,v,1);
            else if(y)mdf(y,u,1);
            else{
                if(p[u])mdf(p[u],u,-1),mdf(p[u],v,1);
                else mdf(p[v],v,-1),mdf(p[v],u,1);
            }
            return output();    
        }
        cout<<"-1\n";
    }
}
int main(){
    ios::sync_with_stdio(false); cin.tie(0);

    cin>>T;
    while(T--)solve();

    return 0;
}