// This is based on copyTree2.C, but without the TEvent ...
// Might not work for ROOT versions < 3.02/07. 

void copy() {
   // -- Get old file, old tree and set top branch address
   TFile *oldfile = new TFile("bigfile.root");
   TTree *oldtree = (TTree*)oldfile->Get("h300");

   // -- Disable all branches ...
   oldtree->SetBranchStatus("*",0);

   // -- ... and switch on those you'd like to write out into the new tree
   oldtree->SetBranchStatus("charge",1);
   oldtree->SetBranchStatus("theta",1);
   oldtree->SetBranchStatus("ecal",1);
   oldtree->SetBranchStatus("phi",1);
   oldtree->SetBranchStatus("p",1);
   oldtree->SetBranchStatus("phiatemc",1);
   oldtree->SetBranchStatus("thetaatemc",1);
   oldtree->SetBranchStatus("runnumber",1);

   //-- Create a new file + a clone of old tree in new file
   TFile *newfile = new TFile("smallfile.root","recreate");
   TTree *newtree = oldtree->CloneTree();

   newtree->Print();
   newfile->Write();
   delete oldfile;
   delete newfile;
}