#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int, int>
void solve()
{
    int n;
    cin >> n;
    vector<vector<int>> e(n + 1);
    vector<vector<int>> dp(n + 1, vector<int>(3, 0));

    vector<set<pii>> ans(n + 1);
    // vector<vector<set<pii>>> ans(n + 1, vector<set<pii>>(3));
    for (int i = 1; i <= n - 1; i++)
    {
        int a, b;
        cin >> a >> b;
        e[a].push_back(b);
        e[b].push_back(a);
    }
    bool flag = 1;
    auto dfs = [&](auto dfs, int x, int fa) -> void
    {
        vector<vector<int>> tmp(3);
        for (auto j : e[x])
        {
            if (j == fa)
                continue;
            dfs(dfs, j, x);
            if (!flag)
                break;
            if (dp[j][1])
            {
                tmp[1].push_back(j);
            }
            else if (dp[j][2])
            {
                tmp[2].push_back(j);
            }
            else
            {
                tmp[0].push_back(j);
            }
        }
        if (x != 1 && ((tmp[0].size() % 2 == 1) || (tmp[2].size() || (tmp[1].size() && tmp[0].size()))))
        {
            if (tmp[0].size() % 2)
            {
                dp[x][1] = tmp[0].back();
                tmp[0].pop_back();
            }
            else if (tmp[2].size())
            {
                dp[x][1] = tmp[2].back();
                tmp[2].pop_back();
            }
            else
            {
                dp[x][1] = tmp[0].back();
                tmp[0].pop_back();
            }
        }
        else if (x != 1 && tmp[1].size() && (tmp[0].size() % 2 == 0 || (tmp[2].size() || tmp[1].size() >= 2)))
        {
            dp[x][2] = dp[tmp[1].back()][1];
            ans[x].insert({dp[x][2], x});
            tmp[1].pop_back();
        }
        for (int i = 0; i + 1 < (int)tmp[0].size(); i += 2)
        {
            ans[x].insert({tmp[0][i], tmp[0][i + 1]});
        }
        if (tmp[0].size() % 2)
        {
            if (tmp[2].size())
            {
                ans[x].insert({tmp[0].back(), tmp[2].back()});
                tmp[2].pop_back();
            }
            else if (tmp[1].size())
            {
                ans[x].insert({dp[tmp[1].back()][1], tmp[0].back()});
                tmp[1].pop_back();
            }
            else
                flag = 0;
        }
        for (int i = 0; i < (int)tmp[2].size(); i++)
        {
            ans[tmp[2][i]].erase({dp[tmp[2][i]][2], tmp[2][i]});
            ans[x].insert({dp[tmp[2][i]][2], x});
        }
        for (int i = 0; i < (int)tmp[1].size(); i++)
        {
            ans[x].insert({dp[tmp[1][i]][1], x});
        }
        return;
    };
    dfs(dfs, 1, 0);
    if (!flag)
    {
        cout << -1 << '\n';
    }
    else
    {
        int x = 0;
        for (int i = 1; i <= n; i++)
        {
            x += ans[i].size();
        }
        cout << x << '\n';
        for (int i = 1; i <= n; i++)
        {
            for (auto j : ans[i])
            {
                cout << j.first << ' ' << j.second << '\n';
            }
        }
    }
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int t;
    cin >> t;
    while (t--)
    {
        solve();
    }
}