Why not buy a roll of brown butcher paper from either a teacher's store or Home Depot, and scrunch a 7 foot section up. Unscruntch it and that staple or use another way to fasten it to your wall. Then rip smaller narrower strips and do the same for the limbs. Rip three large triangular sections and attach these for roots. The end result will be a large three dimensional tree on your wall without the mess of paper mache and in about 15 minutes of time, you can still use your construction paper for prayer leaves. You can also use chix wire and form a tube with some smaller tubes for branches and use papier mache with the torn brown paper for an interesting free standing tree. It is a bit more complicated than this and I have a more detailed description of this process if you would like it but I do not think that is what you are looking for at the moment. Have fun.