The problem occured unexpectedly and appears only in one particular .blend file. After shift-a then curve>sapling tree gen no new object is created. Info shows up, pointing three lines in py's and that one object "Cube.013_Cube.000" is not visible (?) or simply missing.
I tried making a copy of that file, then deleting all objects and seeing if it helps, gives the same info. I tried downloading different blender version and still in that one particular file add on seems to have problem, in any other .blend it works perfectly.