To fold a Christmas tree napkin, start with a square napkin. Place the napkin face-down and fold it in half to create a triangle. Then, fold the triangle in half again, creating a smaller triangle. Next, fold one corner of the triangle down and tuck it under the edge of the napkin. Repeat this on the other side, creating the shape of a Christmas tree. Finally, fold the bottom of the napkin up to create a trunk. The result is a cute and festive Christmas tree napkin!