LTrees does not support scaling trees like that. First of all you should double check if PhysX supports a matrix transform when you create the physics object. It might be called "affine transformation," if that's any help. I'd be surprised
if it doesn't support that, but I'm not familiar with PhysX so I wouldn't know.
If that fails, you can modify an .ltree file like this. Find the "Root" tag, delete it, and insert this XML piece instead (only works when the "ref" parameter was set to "root" previously):
<Call ref="root" delta="0"/>
It's written off the top of my head, so it may or may not work. It should scale the tree by 300%. Replace the "3.0" in both Scale and ScaleRadius to the scale factor you want.
In a future release I might add a way to do this more easily, but I have no plans for developing a new version any time soon.
Good luck with your project. I hope this helped.