Heat the slow cooker to low and add the butter. Once the butter is melted, add the marshmallows and heat, stirring occasionally, until the marshmallows are completely melted.
Once the marshmallows are melted. Add the gel food color a little at a time, stirring continually, until you get to your desired color of green and the color is completely incorporated with melted marshmallows.
Stir the rice cereal into the marshmallow mixture (make sure to spray the wooden spoon or spatula well with baking spray to help with the stickiness) stirring well to completely incorporate the color and cereal mixture.
Starting with the largest star cutter, dipped into melted butter (or sprayed with baking spray) press enough of the rice Krispies treat mixture well and into every corner of the star cutter. *Note - spray hands and working surface well with baking spray or rub with melted butter to make the cereal treats easier to work with. Place the largest rice Krispies star onto a serving platter and remove the cutter.
Continue the same process with the additional star cutters and rice cereal mixture, greasing hands and cutters continually during the process. Place each star shape onto a parchment lined baking sheet and remove the cutter for each. *Note - a cake lifter makes the process of moving the stars onto the baking sheets easier.
Once all the stars are finished and on the baking sheet, sculpt a small cone for the top of the tree. Freeze the stars and cone for at least 10 minutes before assembling the tree.
Add the graduated sizes of stars to the largest star (placed on the serving platter) alternating where the points of the stars are so it resembles a pine tree, pressing lightly after the addition of each star.
Once the tree is assembled, shake the confectioners' sugar over the rice Krispies tree to your desired level of coverage.
Cover the tree loosely with plastic wrap and store at room temperature (or chill in the refrigerator) until ready to serve.
Video
Notes
Cover the tree loosely with plastic wrap and store at room temperature (or chill in the refrigerator) until ready to serve.