Error bars with two different sizes of end marker

I would like to make an error bar with two different sized end points in the same plot. I have tried SetEndErrorSize but this causes all the plots in the canvas to increase their end size. How can I do this?

SetEndErrorSize is a global setting you change via gStyle. Therefore when you change it, it apply on all histograms. One way to bypass this you can use the TExec facility:

TExec ex("ex","gStyle->SetEndErrorSize(...);");