#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 5;
#define pii pair<int, int>
vector<int> g[N];
int p[N], vis[N], in[N];
map<pii, int> mp;
void add(int x, int y)
{
    mp[{x, y}] = 1;
    vis[x] = vis[y] = 1;
    p[x] = y, p[y] = x;
}
void dfs(int u, int f)
{
    vector<int> h;
    for (auto v: g[u])
    {
        if (v == f) continue;
        dfs(v, u);
        if (vis[v]) continue;
        h.push_back(v);
    }

    int sz = h.size();
    if (sz & 1)
    {
        for (int i = 1; i < sz; i += 2) add(h[i], h[i + 1]);
        if (f == 0) return;
        mp[{h[0], f}] = 1;
        vis[h[0]] = vis[u] = 1;
        p[h[0]] = f;
        p[f] = h[0];
    }
    else 
    {
        for (int i = 0; i < sz; i += 2) add(h[i], h[i + 1]);
    }
}
void solve()
{
    int n;
    cin >> n;
    for (int i = 0; i <= n; i++) 
    {
        g[i].clear();
        p[i] = vis[i] = in[i] = 0;
    }
    mp.clear();
    for (int i = 1, u, v; i < n; i++) 
    {  
        cin >> u >> v;
        g[u].push_back(v), g[v].push_back(u);
        in[u]++, in[v]++;
    }
    int s = 0;
    for (int i = 1; i <= n; i++)
    {
        if (in[i] % 2 == 0) 
        {
            s = i;
            break;
        }
    }
    if (!s) 
    {
        cout << -1 << '\n';
        return;
    }
    dfs(s, 0);
    
    for (auto i: g[s])
    {
        if (vis[i] == 0) 
        {
            if (p[s])
            {
                mp[{p[s], s}] =  mp[{s, p[s]}] = 0;
                mp[{p[s], i}] = 1;
            }
            else if (p[i])
            {
                mp[{p[i], i}] = mp[{i, p[i]}] = 0;
                mp[{s, p[i]}] = 1;
            }
            else 
            {
                cout << -1 << '\n';
                return;
            }
        }
    }
        
    vector<pii> ans;
    for (auto [i, w]: mp) 
        if (w) ans.push_back(i);
    cout << ans.size() << '\n';
    for (auto [x, y]: ans) cout << x << ' ' << y << '\n';
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    int T; cin >> T;
    while (T--) solve(); 
}