Pls. see the attached.
If the treegrid is empty origionally( only with header on), and switch to load a nonempty treegrid, all is ok;
If the treegrid is nonempty origionally, and switch to load an empty treegrid (only width header on), then error arise, say style problem.
The issue appears when there’s hidden column in the nonempty treegrid.
If change the column hidden property to false, everything is ok.