Irrlicht Engine

Hello,
I have loaded two models here, and I want to make their collision.
The collision is ok, but the models looks more fat than what they really are.

I tried what is shown at API:

core::aabbox3d<f32> box = yourSceneNode->getBoundingBox();
core::vector3df radius = box.MaxEdge - box.getCenter();

but the radius returned is bigger than the real one.

Does it work only for balls and boxes?
I have a tree, and it´s much bigger on Y axis than in X or Z



Thanks

Here is a rar containing all the code:
http://www.vinoblesse.nl/~didier/boomwar.rar