{
  gROOT->Reset();

  Int_t Evnt;

  TFile *file_total = new TFile("total.root","RECREATE");

  TFile *file_1 = new TFile("file1.root","READ");

  TTree *tree_1 = (TTree*)file_1->Get("tree1")->Clone("tree_1");
  tree_1->SetBranchAddress("Evnt",&Evnt);

  //Build the indexer according to Evnt branch
  tree_1->BuildIndex("Evnt");

  TFile *file_2 = new TFile("file2.root","READ");

  TTree *tree_2 = (TTree*)file_2->Get("tree2")->Clone("tree_2");

  //Build the indexer according to Eventno branch 
  // (should  be same as Evnt for previous tree)
  tree_2->BuildIndex("Eventno");

  file_total->cd();
  TTree *tree_temp = tree_temp=tree_1->CopyTree("");
  tree_temp->AddFriend(tree_2);
  //  tree_temp->SetName("tree_temp");

  //No entries are copied just the structure, correct?
  TTree *tree_total = tree_temp->CopyTree("","",0,0);

  // The number of Entries of this tree 
  // is be the bigger of the two friends,
  // correct ?
  for(int i=0; i< tree_temp->GetEntries(); i++){
    tree_1->GetEntry(i);
    tree_2->GetEntryWithIndex(Evnt);
    tree_total->Fill();
  }
  tree_total->SetName("tree_total");
  file_total->cd();
  tree_total->Write();
}