ih, i duno about tuts for modeling a tree, if u wana model it id start with making a rigid circular kinda shape using the create poly tool, then extrued it upwards add horizontal divisions then move verts around, add branches and stuff, leaves wud be harder but u cud just make one and copy/paste it, or maybe just make a flat square plane and in photoshop draw and paint the leaves and then use a transparency map or something to make it look like there are individual leaves, if u dont wana do all that theres some trees in the maya visor