int makeHisto()
{
  TFile* file = new TFile("file.root","RECREATE");
  TDirectoryFile* dir = (TDirectoryFile*)file->mkdir("dir");
  dir->cd();
  
  TH1F* h = new TH1F("h","",100,-5,5);
  for (int i=0;i<10000;i++) h->Fill(gRandom->Gaus());

  file->Write();
  file->Close();
  
  return 0;
}