This is a simple method to create a realistic looking tree for any stage or theatrical production with easy to find products and it's very cheap to make, too. :)
Step 1: Base and Structure
I started by screwing some scrap wood strips in a tree-like form. This doesn't need to be pretty, but it should be strong. It's going to hold the rest of the pieces. I put a three legged base on the bottom so it didn't lean or fall over and also screwed it into the wooden platform as well.
Next, I ripped up some old cardboard boxes and rolled them so that it took the curved form needed. I pieced it up the trunk of the tree and stapled it to the wood from behind with a staple gun. Anything that was uneven or odd looking, I covered in duct tape to smooth it out and make it stay together as well.
Step 2: Texture
Next, I ripped up some shipping foam that I got in the mail from a package. It was all recycled material. I ripped it in rough strips and stapled it to the cardboard. Then I used "great stuff" spray foam from Walmart to create new strips up and in between the thicker strips. It takes a little bit to dry, but once it's done, you're ready to add the paper mache.
I used brown packing paper. You can buy it in rolls at walmart. Mix up some flour, water, and glue, dip the paper in and then flatten it against the texture on the tree. Go all the way up until the whole tree is covered. Then let it dry. (a fan helps)
Step 3: Final Stage
After the paper is dry, paint it however you want. I darkened the lower levels and dry brushed the higher texture with a lighter color brown. I added some green grass that we had already and next I have to get some leaves, but it's mostly done. If you add some side lighting, it looks pretty cool.
The whole project took about 2 days to finish, but it's not difficult. Good luck!