void test() { TTree *tree = new TTree("myTree","Testing tree"); Double_t x,y,z; tree->Branch("x",&x,"x/D"); tree->Branch("y",&y,"y/D"); tree->Branch("z",&z,"z/D"); for(Int_t i=0; i<1; i++) { x = gRandom->Rndm(); y = gRandom->Rndm(); z = gRandom->Rndm(); tree->Fill(); } TFile *fout = TFile::Open("tree.test.root","recreate"); tree->Write(); cout << fout->GetCompressionFactor() << endl; fout->Close(); }