Prepare baking sheet by rubbing a small amount of butter or cookie spray on the base of the pan.
Melt butter on low then add in five and a half cups miniature marshmallows. Stir often until fully melted.
Stir in rice krispies into melted marshmallow mixture until well incorporated. Line a baking sheet with parchment paper and pour out cereal mixture onto the parchment paper. Press down with a spatula. Let dry 30 minutes.
Cut out rice krispies with a tree cookie cutter. lace back on parchment paper.
Melt green candy melts as directed on the package but do this in a piping bag. Pipe around the edges and across point to point of the Christmas tree.
Notes
Store treats at room temperature in an airtight container layered with waxed paper up to a week.