To make a pop-up Christmas tree card, you'll need the following supplies: a piece of cardstock, scissors, a pencil, a ruler, and glue. First, cut out a rectangle from the cardstock, and fold it in half to create a card. Next, use a pencil and ruler to draw two diagonal lines from the corners of the card to the center. Cut along these lines, but leave a small tab at the center point. Then, fold the tabs up to create a 3D Christmas tree shape. Use glue to secure the tabs in place, and decorate your pop-up Christmas tree card with festive colors and