Preheat the oven to 350 degrees and line a 9x9 baking dish with parchment paper.
Combine the vegetable oil, sugar and vanilla extract.
Whisk in the eggs.
Slowly fold in the flour, cocoa powder and baking powder.
Pour the batter into the prepared baking dish.
Bake for 25-30 minutes.
Remove from the oven and let cool.
Line a baking sheet with parchment paper.
Gently lift the brownies from the baking dish and use the triangle cookie cutter to carefully cut the brownies as close as possible and place on the prepared baking sheet.
Gently insert a pretzel stick into the base of each Christmas tree.
Attach the Petal tip to the the icing pouch and gently squeeze the icing from pouch in a back and forth motion going from the top of the brownie to the bottom.
Add a star sprinkle on top and multi-colored sprinkles to the tree.