Now that you've got two halves, glue them together or staple them. This is kinda tricky so I couldn't take a picture of me glueing the halves. When glueing the tops you should squeeze them for a while because they tend to unstick
There You Have a Tree!!!
You can use some construction paper of some sort or cylinder to hold the tree up.
You can make other things to make it look good. You could try painting it, adding LED's, use your imagination.