QTreeView: expand(), expandAll(), setExpanded() not work

[wysota]

It is hard to reproduce it, since my code is a little more.
Any suggestion to make it work immediately, like calling some APIs.

If you can't reproduce the problem with a small example then it is likely that the problem originates in your own code and if so, then without knowing where the problem lies it is hardly possible to suggest a solution. I suggest you spend 20 minutes trying to assemble a minimal compilable example reproducing the problem.