#include <bits/stdc++.h>
#define For(i,x,y) for (int i=(x);i<=(y);i++)
#define mp make_pair
#define fi first
#define se second
#define pb push_back
#define siz(x) ((int)x.size())
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pa;
using namespace std;

inline ll read(){
    ll x;
    scanf("%lld",&x);
    return x;
}

const int N = 3e5+10;
int n;
vector<int>e[N];

vector<pa>ans;
int f[N];
inline void dfs0(int u,int fa){
    vector<int>son;
    for (auto v:e[u]) if (v!=fa){
        dfs0(v,u);
        if (f[v]) son.pb(v);
    }
    while (siz(son)>=2){
        int a=son.back();
        son.pop_back();
        int b=son.back();
        son.pop_back();
        ans.pb(mp(a,b));
    }
    if (son.empty()){
        f[u]=1;
    } else {
        f[u]=0;
        assert(fa);
        ans.pb(mp(son[0],fa));
    }
}

int p,g[N];
inline void find(int u,int fa){
    if ((siz(e[u])-(fa>0))%2) p=u;
    for (auto v:e[u]) if (v!=fa) find(v,u);
}
inline void dfs1(int u,int fa){
    vector<int>son;
    for (auto v:e[u]) if (v!=fa){
        dfs1(v,u);
        if (f[v]) son.pb(g[v]);
    }
    while (siz(son)>=2){
        int a=son.back();
        son.pop_back();
        int b=son.back();
        son.pop_back();
        ans.pb(mp(a,b));
    }
    if (son.empty()){
        f[u]=1;
        g[u]=u;
    } else {
        if (p==u){
            f[u]=1;
            g[u]=son[0];
            return;
        }
        f[u]=0;
        ans.pb(mp(son[0],fa));
        if (!fa) ans.clear();
    }
}

inline void solve(){
    n=read();
    For(i,1,n) e[i].clear();
    For(i,1,n-1){
        int x=read(),y=read();
        e[x].pb(y),e[y].pb(x);
    }
    if (n==2){
        puts("-1");
        return;
    }
    if (n%2){
        ans.clear();
        dfs0(1,0);
        printf("%d\n",siz(ans));
        for (auto [x,y]:ans) printf("%d %d\n",x,y);
    } else {
        bool flag=0;
        For(i,1,n) if (siz(e[i])%2==0){
            flag=1;
            break;
        }
        if (!flag){
            puts("-1");
            return;
        }
        int rt=1;
        p=0,find(rt,0);
        assert(p&&p!=rt);
        ans.clear();
        dfs1(rt,0);
        if (ans.empty()){
            puts("-1");
            return;
        }
        printf("%d\n",siz(ans));
        for (auto [x,y]:ans) printf("%d %d\n",x,y);
    }
}

int main(){
    //freopen("i.out","w",stdout);
    int T=read();
    while (T--) solve();
}
/*
4
4
1 2
1 3
3 4
4
1 2
2 3
3 4
4
1 2
1 3
1 4
6
1 2
1 4
2 6
2 3
3 5

*/