I made the trees using a wrapping paper tube and a light weight fabric that I purchased from here.
First I covered the tube in white fabric and used a black fabric marker to make the stripes. I hot glued a 4" Styrofoam ball to the the end of the tube. The top of the tree was made by cutting fabric into squares. I did not measure them as I cut. The squares were roughly 5". Using straight pins at the center of a square I pinned individual squares all over the Styrofoam ball.
*This picture shows a bowl for the base. It was not stable enough for the tree. A new base is in the works. An update will follow soon!
I will post the book display once the base for the trees is finished. My wonderful husband is designing a base that will be steady enough to hold the trees. Pictures will be up later this week.
Here's the book display with the Truffula Trees: