Thanks for your prompt response. Do you mean to say, I should define one multigraph and add all TGraph (for expected and observed values) and TGraphAssymErrors ( for 1sigma and 2sigma bands) with that? Or I should define multiple TMultiGraph, separately for TGraph and TGraphAssymErrors?
I suppose one for all should work, maybe depending on the draw options, if it doesn’t work maybe you can try drawing the multigraphs on top of each other; just try and experiment if needed