#include <cstdio>
#include <algorithm>
#include <vector>
#include <utility>
#include <cstring>

using namespace std;

const int max1 = 3e5;

int T, n;

struct Node
{
    int v, next;
}edge[max1 * 2 + 5];
int head[max1 + 5], total;

int f[max1 + 5], deep[max1 + 5];
vector <int> son[max1 + 5];
vector < pair <int, int> > ans;

void Add ( int u, int v )
{
    edge[++total].v = v;
    edge[total].next = head[u];
    head[u] = total;
    return;
}

bool Cmp ( const int &x, const int &y )
{
    return deep[x] < deep[y];
}

void Dfs ( int now, int fa )
{
    deep[now] = deep[fa] + 1;
    son[now].clear();
    for ( int i = head[now]; i; i = edge[i].next )
    {
        int v = edge[i].v;
        if ( v == fa )
            continue;
        
        Dfs(v, now);
        
        if ( f[v] )
            son[now].push_back(f[v]);
        else
            son[now].push_back(v);
    }

    sort(son[now].begin(), son[now].end(), Cmp);

    int siz = son[now].size() - 1;

    f[now] = 0;
    if ( siz >= 0 )
    {
        if ( siz & 1 )
        {
            if ( now == 1 )
            {
                for ( int i = 0; i <= siz; i += 2 )
                    ans.push_back(make_pair(son[now][i], son[now][i + 1]));
            }
            else
            {
                for ( int i = 0; i <= siz - 2; i += 2 )
                    ans.push_back(make_pair(son[now][i], son[now][i + 1]));

                if ( deep[son[now][siz - 1]] > deep[now] + 1 )
                {
                    ans.push_back(make_pair(son[now][siz - 1], now));
                    f[now] = son[now][siz];
                }
                else if ( deep[son[now][siz]] > deep[now] + 1 )
                {
                    ans.push_back(make_pair(son[now][siz], now));
                    f[now] = son[now][siz - 1];
                }
                else
                {
                    ans.push_back(make_pair(son[now][siz - 1], son[now][siz]));
                }
            }
        }
        else
        {
            f[now] = son[now].back();
            
            for ( int i = 0; i <= siz - 1; i += 2 )
                ans.push_back(make_pair(son[now][i], son[now][i + 1]));
        }
    }

    // printf("now = %d f = %d\n", now, f[now]);

    return;
}

void Work ()
{
    scanf("%d", &n);

    total = 0;
    memset(head, 0, sizeof(int) * (n + 1));

    int u, v;
    for ( int i = 2; i <= n; i ++ )
    {
        scanf("%d%d", &u, &v);
        Add(u, v), Add(v, u);
    }

    ans.clear(); deep[0] = -1;
    Dfs(1, 0);

    if ( f[1] && deep[f[1]] > 1 )
        ans.push_back(make_pair(1, f[1])), f[1] = 0;

    if ( f[1] )
        printf("-1\n");
    else
    {
        printf("%lu\n", ans.size());
        for ( auto v : ans )
            printf("%d %d\n", v.first, v.second);
    }
    return;
}

int main ()
{
    scanf("%d", &T);
    while ( T -- )
        Work();

    return 0;
}