This bug affects only the OpenGL driver.

For increased precision, A5 uses nonlinear z-buffering, referred to as a "w-buffer" in some publications. Nonlinear buffering means that the precision increases when you are close to the object, but decreases when you are far from it. This could happen in your case if the tree is quite far away. Maybe you are using zoom here. The solution is to go closer to the object, while zooming out.