I was making this pillow from scratch so I purchased a 12"x16" pillow form and the white cotton fabric to make a cover. I pulled out my sewing guide - Martha Stewart's Encyclopedia of Sewing and Fabric Crafts: Basic Techniques for Sewing, Applique, Embroidery, Quilting, Dyeing, and Printing, plus 150 Inspired Projects from A to Z - and followed the directions to make an envelope-backed pillow cover so that I can change the cover after different holidays. It was fairly easy!
Then I picked three print fabrics that look good together and could be used for 'trees'. Walking on the crazy edge of crafting, I just cut out three triangles without using a template and hoped for the best. I didn't worry too much about perfectly straight lines.
Because the pillow cover was already sewn together, I chose to glue the trees and stumps directly on the pillow using Dritz 6.51 Ounce Quilting Spray On Heat Set Adhesive and an iron. Then I used the tip of the scissors and frayed the edges of the trees.