void demo()
{
  // no problem with TFile::Open
  auto f = TFile::Open("root://eosuser.cern.ch//eos/user/a/angabrie/TEST/v20mEpsilon//mc16a//Nominal/mc16_13TeV.345060.PowhegPythia8EvtGen_NNLOPS_nnlo_30_ggH125_ZZ4l.root");
  f->Get("tree_incl_all");
  auto t = (TTree*) f->Get("tree_incl_all");
  // triggers actual reading of the tree
  std::cout << t->GetEntries() << std::endl;

  auto tc = new TChain("tree_incl_all");
  // works fine
  tc->Add("root://eosuser.cern.ch//eos/user/r/rowang/public/mc16_13TeV.345060.PowhegPythia8EvtGen_NNLOPS_nnlo_30_ggH125_ZZ4l.root");
  // those two don't work
  tc->Add("root://eosuser.cern.ch//eos/user/a/angabrie/TEST/v20mEpsilon//mc16a//Nominal/mc16_13TeV.345060.PowhegPythia8EvtGen_NNLOPS_nnlo_30_ggH125_ZZ4l.root");
  tc->AddFile("root://eosuser.cern.ch//eos/user/a/angabrie/TEST/v20mEpsilon//mc16a//Nominal/mc16_13TeV.345060.PowhegPythia8EvtGen_NNLOPS_nnlo_30_ggH125_ZZ4l.root");
  // triggers actual reading of the tree
  std::cout << tc->GetEntries() << std::endl;
}