void TestCode(){
  //create file
  TFile *f  = new TFile("TestNTuple.root","RECREATE");

  //create ttree and initialize branches
  TTree *tree = new TTree("tree","tree");
  Float_t val,weight;
  tree->Branch("val",&val,"val/F");
  tree->Branch("weight",&weight,"weight/F");

  //fill a few entries into this ntuple
  val=2;
  weight=0.1;
  cout<<"Filling Entry: val="<<val<<"  weight="<<weight<<endl;
  tree->Fill();

  val=2;
  weight=0.1;
  cout<<"Filling Entry: val="<<val<<"  weight="<<weight<<endl;
  tree->Fill();

  val=2;
  weight=0.2;
  cout<<"Filling Entry: val="<<val<<"  weight="<<weight<<endl;
  tree->Fill();

  cout<<endl<<endl<<"CorrectBinError:"<<endl;
  float errCorrect = pow( 0.1*0.1 + 0.1*0.1 + 0.2*0.2, 0.5);
  cout<<errCorrect<<endl;


  f->cd();

  ///////////////////////////////
  //Draw 1d histogram with error option set to compute errors using Sumw2()
  ///////////////////////////////
  cout<<endl<<endl<<"1D HIST"<<endl;

  tree->Draw("val>>h0(5,0,5)","weight","e");
  TH1D *h0 = (TH1D*)gDirectory->Get("h0");
  h0->SetLineColor(2);
  h0->Draw("hist");

  //loop over bins in histogram and inspect the bin content and error value
  int nx = h0->GetNbinsX();
  for(int i=0; i<nx; i++){
          double bcon = h0->GetBinContent(i);
          double berr = h0->GetBinError(i);
          cout<<"h1: BinNumber="<<i<<"  BinContent="<<bcon<<"  BinError="<<berr<<endl;
  }




  ///////////////////////////////
  //Draw 2d histogram with error option set to compute errors using Sumw2()
  ///////////////////////////////cout<<"2D HIST"<<endl;
  cout<<endl<<endl<<"2D HIST"<<endl;

  tree->Draw("val:val>>h1(5,0,5,5,0,5)","weight","e");
  TH2D *h1 = (TH2D*)gDirectory->Get("h1");
  h1->SetLineColor(2);
  h1->Draw("hist");

  //loop over bins in histogram and inspect the bin content and error value
  int nx = h1->GetNbinsX();
  int ny = h1->GetNbinsY();
  for(int i=0; i<nx; i++){
      for(int j=0; j<ny; j++){

          double bcon = h1->GetBinContent(i,j);
          double berr = h1->GetBinError(i,j);

          cout<<"h1: BinNumber(X)="<<i<<"  BinNumber(Y)="<<j<<"  BinContent="<<bcon<<"  BinError="<<berr<<endl;

  }
  }

}