How can I engender fictitious trees? I am a high school professor and I want to make a...

I am a high school professor and I want to make a couple of realistic-looking hardwood trees for a reading corner in my classroom. I already hold the fake leaves that I'll be using, but I could use some suggestions on how I might make the trunk and branches of the tree. Thanks.
Answers:    Trunk - At your local hardware store, you can find circular molds used for concrete. Simply cut one of those contained by half, attach to the wall and paint it brown. ( For a cute touch, you could cut a little hole out of the trunk and install a shelf to store books and trinkets)

Limbs - Real, actual limb will probably work best for this. Just gather some up out of the yard and drill holes into your "trunk." Insert the limb into the trunk and secure with hot cement or super glue.
Hmm my first thought would be getting just plain cardboard and shaping it but I do not know how sturdy that would be. My subsequent thought would be real wood. You could try sawing tree silhouettes out and putting them on your wall and somehow create branches coming out of it therefore giving it the 3-d effect. Or if sawing isnt something you want to look into, check out Balso wood. It is easier to shape and the wood is completely soft. You usually can find this in hobby stores or craft stores. At a big box home store they sell fencing explicitly half logs. Drill some holes in it and insert fresh cut willow branches. Willow won't carry as brittle as regular branches. You can find them usually in wet areas close by a bigger willow. Add your leaves. I might even stand it on an old type christmas tree stand, 2 pieces of wood on bottom making a cross. How about using that grass rug around bottom to stow cross. Good luck!