void readtree() {

  TFile *f = TFile::Open("events.root");
  TTree *tree = (TTree*)f->Get("Events");
  Float_t var2;
  tree->SetBranchAddress("var2", &var2);

  Int_t nentries = tree->GetEntries();
  for (Int_t i=0;i<nentries;i++) {
    tree->GetEntry(i);
    cout << var2 << endl;
  }
}