Just open the model, go Modules > Sequense editor.
There should appear Bone, Anims and Movement editor thingies for you to use,
From Bones you can create bones and attach verticles to them. Your model should have a main bone, which has all verticles attached to it.
Select Anims and make sure that model has Birth, Stand and Death animations. Stand needs to be looping, others non looping.
Select Stand, go to Movement and select your main bone, select Rotate tool and start to rotate the model.
First and last frame must be identical. There are copy and paste under Frames. Select few spots from that timeline ( so called key frames ) and give them different rotations and you get your tree to rotate.
For death and birth you can use Scale tool and scale main bone so small that model dissapears. Also download Magos Model editor and learn to use particles, so you can add some cool looking impact effects to death aniamtion.
You have an MPQ editor? If so open war3x.mpq and browse it's contents. I'm not exactly sure about the location of the images but it should be there for every race. Then it's just a simple matter of "over linkining" the .BLP's with the Import Editor.