Unable to display the histogram entries and standard deviation

[dastudillo]

You need to create your own 2D histogram (so check the bins you need in x and y) and fill it when you do tree->Draw.

Can't put TPaveStats box on a histogram

Yes because at the 2nd execution the histogram already created. I works also without drawing option if you create the histogram before doing TTree::Draw. root [0] TH2F *h2 = new TH2F("h2","h2",10,-10,10,10,-10,10) root [1] ntuple->Draw("px:py>>h2")