Whenever I try to render a tree it's 'trunk' (think it's called like that) gets in a square-shape during the rendering process. as you can see below. What should I do??
I've just tried the same settings as you but I don't get that result.
The Tree render uses the GPU so you could try different GPU settings (basic, normal, advanced) in Preferences > Performance
Do you actually have a selection or a vector path in your document? Some of those renderers will follow contours. Certainly looks like that in your image.
Mylenium - well spotted - I tried again with a rectangular path and got this
Retrieving data ...