I just tinkered with this for some 20 minutes. Instead of moving the camera around the tree, I just tilted the earth layer to let it lie flat so it could be rotated around the axis of the tree layers. To make things easy, I created the first bone/vector layer pair, duplicated and flipped it, then duplicated both again, put them into a group and turned this group layer 90°.

http://www.slowtiger.de/examples/baumtest.swf
Since anything on a layer lacks volume, I can't think of a possible purpose for this trick, at least not within my range of styles.