#include<cstdio>
#include<iostream>
#include<vector>
#include<algorithm>
#define RI register int
#define CI const int&
using namespace std;
const int N=200005;
int t,n,m,x,y;
struct DSU
{
    vector <int> fa,pre; vector <vector <int>> G;
    vector <pair <int,int>> E;
    inline void init(CI n)
    {
        fa.resize(n); pre.resize(n); G.resize(n); E.clear();
        for (RI i=0;i<n;++i) G[i].clear(),pre[i]=-1,fa[i]=i;
    }
    inline int getfa(CI x)
    {
        return fa[x]!=x?fa[x]=getfa(fa[x]):x;
    }
    inline bool query(CI x,CI y)
    {
        return getfa(x)==getfa(y);
    }
    inline void merge(CI x,CI y)
    {
        //printf("(%d,%d)\n",x,y);
        fa[getfa(x)]=getfa(y);
        E.push_back({x,y});
        G[x].push_back(y); G[y].push_back(x);
    }
    inline void findpath(CI now,CI tar,vector <int>& path)
    {
        if (now==tar)
        {
            for (int x=tar;x!=n;x=pre[x]) path.push_back(x);
            reverse(path.begin(),path.end());
            return;
        }
        for (auto to:G[now]) if (pre[to]==-1) pre[to]=now,findpath(to,tar,path);
    }
}D[N];
int main()
{
    //freopen("F.in","r",stdin);
    for (scanf("%d",&t);t;--t)
    {
        scanf("%d%d",&n,&m);
        int tot=(m+n-2)/(n-1);
        for (RI i=1;i<=tot;++i) D[i].init(n);
        for (RI i=1;i<=m;++i)
        {
            scanf("%d%d",&x,&y); --x; --y;
            int l=1,r=tot,ret=tot+1;
            while (l<=r)
            {
                int mid=l+r>>1;
                if (!D[mid].query(x,y)) ret=mid,r=mid-1; else l=mid+1;
            }
            if (ret<=tot) D[ret].merge(x,y);
        }
        if (D[tot].E.empty()) { puts("-1"); continue; }
        auto [u,v]=D[tot].E.back();
        printf("%d %d\n",u+1,v+1);
        for (RI i=1;i<=tot;++i)
        {
            vector <int> path;
            D[i].pre[u]=n;
            D[i].findpath(u,v,path);
            printf("%d ",path.size());
            for (auto x:path) printf("%d ",x+1);
            putchar('\n');
        }
    }
    return 0;
}