void AddBranch() {
  TFile f("Fakes_Muons.root","update");
  int isMuonStream;
  TTree *t = (TTree*)f.Get("mini");
  TBranch *newBranch = t->Branch("isMuonStream",&isMuonStream,"isMuonStream/i");
  //read the number of entries in the t3
  int nentries = (int)t->GetEntries();
  for (int i = 0; i < nentries; i++){
    isMuonStream = 1;
    newBranch->Fill();
  }
  t->Write("",TObject::kOverwrite);     // save only the new version of the tree
  f.Close();

  TFile f2("Fakes_Egamma.root","update");
  TTree *t2 = (TTree*)f2.Get("mini");
  TBranch *newBranch2 = t2->Branch("isMuonStream",&isMuonStream,"isMuonStream/i");
  //read the number of entries in the t3
  int nentries2 = (int)t2->GetEntries();
  for (int i = 0; i < nentries2; i++){
    isMuonStream = 0;
    newBranch2->Fill();
  }
  t2->Write("",TObject::kOverwrite);     // save only the new version of the tree

}