Preheat the oven to 400 degrees. Position both pieces of puff pastry on top of one another on a parchment-lined baking sheet. Trim the edges to form a Christmas tree shape from the square.
Remove the top layer and spread the Nutella onto the bottom layer. Place the other sheet back on top. Use a knife to cut 1” strips up each side of the dough to make the tree branches. Take the end of each strip and twist it several times.