void makeSmallerTuple() {
    gSystem->Load("JansEvent_cc");
    JansEvent* j = new JansEvent;
    TFile f("file.root");
    TTree* tin = (TTree*) f.Get("evtTree");
    tin->SetBranchAddress("event", &j);
    TFile fout("xCINT.root", "recreate");
    TTree t("bugMe", "Sample events");
    t.Branch("event", "JansEvent", &j, 32000, 99);

    for (int iEv=0; iEv<3; ++iEv) {
        tin->GetEvent(iEv);
        t.Fill();
    }
    t.Write();
//    fout.Close();
}