import java.util.*;
import java.io.*; 
import java.text.*;
//Solution Credits: Taranpreet Singh
class Editorial{
    //SOLUTION BEGIN
    void solve(int TC) throws Exception{
        int n = ni();
        int[][] g = new int[n][n];
        for(int i = 1; i*2<= n*n-n; i++){
            int u = ni()-1, v = ni()-1;
            g[u][v] = i;
            g[v][u] = -i;
        }
        int x = n;
        while(x>1){
            if((x&1)==1){
                pn(-1);
                return;
            }
            x>>=1;
        }
        int[] winner = new int[n];
        int f = 1;
        for(int i = 0; i< n; i++)winner[i] = i;
        x = n;
        boolean[] keep = new boolean[(n*n-n)/2+1];
        while(x>1){
            for(int i = 0; i< n; i+=2*f){
                int u = winner[i], v = winner[i+f];
                if(g[u][v]<0){
                    int t = u;u=v;v=t;
                }
                keep[g[u][v]] = true;
                winner[i] = u;
            }
            f*=2;
            x/=2;
        }
        pn((n*n-n)/2-(n-1));
        for(int i = 1; i< keep.length; i++)if(!keep[i])p(i+" ");pn("");
    }
    //SOLUTION ENDS
    long mod = (long)1e9+7, IINF = (long)1e17;
    final int MAX = (int)1e6+1, INF = (int)2e9, root = 3;
    DecimalFormat df = new DecimalFormat("0.000000000000");
    double PI = 3.1415926535897932384626433832792884197169399375105820974944, eps = 1e-8;
    static boolean multipleTC = true, memory = false;
    FastReader in;PrintWriter out;
    void run() throws Exception{
        in = new FastReader();
        out = new PrintWriter(System.out);
        int T = (multipleTC)?ni():1;
        //Solution Credits: Taranpreet Singh
        for(int i = 1; i<= T; i++)solve(i);
        out.flush();
        out.close();
    }
    public static void main(String[] args) throws Exception{
        if(memory)new Thread(null, new Runnable() {public void run(){try{new Editorial().run();}catch(Exception e){e.printStackTrace();}}}, "1", 1 << 28).start();
        else new Editorial().run();
    }
    long gcd(long a, long b){return (b==0)?a:gcd(b,a%b);}
    int gcd(int a, int b){return (b==0)?a:gcd(b,a%b);}
    int bit(long n){return (n==0)?0:(1+bit(n&(n-1)));}
    void p(Object o){out.print(o);}
    void pn(Object o){out.println(o);}
    void pni(Object o){out.println(o);out.flush();}
    String n(){return in.next();}
    String nln(){return in.nextLine();}
    int ni(){return Integer.parseInt(in.next());}
    long nl(){return Long.parseLong(in.next());}
    double nd(){return Double.parseDouble(in.next());}

    class FastReader{
        BufferedReader br;
        StringTokenizer st;
        public FastReader(){
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        public FastReader(String s) throws Exception{
            br = new BufferedReader(new FileReader(s));
        }

        String next(){
            while (st == null || !st.hasMoreElements()){
                try{
                    st = new StringTokenizer(br.readLine());
                }catch (IOException  e){
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        String nextLine(){
            String str = "";
            try{    
                str = br.readLine();
            }catch (IOException e){
                e.printStackTrace();
            }   
            return str;
        }
    }
}