#include "TFile.h"
#include "TTree.h"
#include "TMath.h"

void filltree()
{
  TTree::SetMaxTreeSize(10*Long64_t(2000000000));
  TFile *f = new TFile("testselector.root","RECREATE");
  TTree *mytree = new TTree("mytree","");
  Float_t a;
  Long64_t maxentries;
  
  maxentries=(Long64_t)pow(2,32);
  a=0;

  mytree->Branch("a",&a,"a/F");

  for(Long64_t i=0; i<maxentries; i++){
    mytree->Fill();
  } 
 
  mytree->Write();
}