Prepare pizza crust according to package directions.
On lightly floured work surface, roll out dough into large rectangle, about 1/4 inch (5 mm) thick.
Using large Christmas tree cookie cutter, cut out 12 Christmas trees, rerolling dough as needed. Transfer tree pizzas to 2 large parchment paper–lined baking sheets, about 2 inches (5 cm) apart.
Spread sauce over each pizza; sprinkle with cheese. Garnish with pepperoni and green pepper.
Bake according to package directions, about 10 to 15 minutes, or until crust is golden brown. Let cool for 5 minutes before serving.