Meanwhile, place a piece of cooking parchment or waxed paper on cookie sheet. Draw 1 1/2- to 2-inch tree outlines or trace around 2-inch tree-shaped cookie cutter, leaving 1/2 inch space between each tree. Center toothpick at bottom of and 1/2 inch into each tree outline. In 1-quart saucepan, heat 1 cup chocolate chips and the shortening over low heat, stirring constantly, until chips are melted. Pour chocolate into decorating bag fitted with plain tip or resealable plastic bag; snip one corner. Starting at top of each tree outline, pipe chocolate over tree and end of toothpick within tree; fill center with random, squiggly lines. Refrigerate until chocolate hardens. Gently remove trees from paper; refrigerate until serving.