So I've settled on this for now. In hindsight it seems pretty simple, but maybe it will be helpful for someone new who digs up this thread in the future.

I set up a material for the tree, and added the line:

effect = "technique { pass { AlphaTestEnable = True; ZWriteEnable = True; AlphaBlendEnable = False; CullMode = None;} }";

Thanks to everyone for all their help! I think this does what I wanted originally. I won't reply to this thread anymore as I have started a new one in "shaders" for more complicated tree techniques.