Custom trees on terrain

Hi community,
I’m not sure if it’s the right place to ask this question because I’m newbie in Unity.

Is it possible to use our custom trees instead of built-in trees in Unity?

I would like to have really custom trees ^^ For instance, I want particles attach to my tree. (Like this : http://www.armaghia.fr/temps/dl6/dl6_1.jpg, I made it in Ogre) Is it possible ? If I parent a particle emitter to my tree, will it work ? Ideas ?