void simpletree() {

TFile* f = TFile::Open("events.root", "RECREATE");
TTree* t = new TTree("Events","Event Tree");
Int_t           var1;
Float_t         var2;
Float_t         var3;
 t->Branch("var1",  &var1, "var1/I");
 t->Branch("var2",  &var2, "var2/F");
 t->Branch("var3",  &var3, "var3/F");

 var1=5; var2=3.1; var3=10.;
 t->Fill();
   
 var1=1; var2=7; var3=4.5;
 t->Fill();

 t->Print();
 t->Show(1);

 t->Write();
 f->Close();
}