Preheat the oven to 350°F (180°C).
Prepare the puff pastry: Unroll the cold puff pastry on a baking sheet lined with parchment paper. Cut out Christmas tree shapes using a cookie cutter. Arrange them on the sheet, leaving space between each.
Make the sauce: In a bowl, mix together the tomato passata, salt, olive oil, and oregano (if using). Adjust seasoning to taste.
Assemble the pizza bites: Spoon a small amount of sauce onto each tree-shaped puff pastry. Spread evenly, leaving a small border. Top with shredded mozzarella cheese.
Bake: Place the baking sheet in the lower rack of the oven and bake for 15 minutes, or until golden brown and the cheese is melted.
Serve immediately: Enjoy hot for the best flavor!