To fold a napkin into a Christmas tree, start with a square napkin. Fold one corner of the napkin to the opposite corner, creating a triangle. Then, fold the bottom edge of the triangle up, creating a rectangle. Now, fold the right and left sides of the rectangle in towards the middle, so that they meet in the middle. Finally, fold the top edge of the rectangle down, so that the tip of the triangle is pointing down. You should now have a triangular napkin with the tip pointing down, which looks like a Christmas tree.