Line a 9x13-inch baking dish with parchment paper or lightly spray with nonstick cooking spray. Set aside.*I recommend lining with parchment paper and leaving an overhang, so it's easier to lift the treats out to cut them into the tree shape. In a large pot, over medium-low heat, melt the butter.
4 tablespoons butter
Once the butter is melted add in the mini marshmallows and stir constantly until they're completely smooth and melted.
1 bag (10 oz) mini marshmallows
Remove the pot from the heat and immediately stir in the vanilla extract and a 2-3 drops of the green gel food coloring (or more as needed). Stir until the color is even.
1 teaspoon vanilla extract, green gel food coloring
Add in the Rice Krispies cereal and stir until the cereal is coated well and combined thoroughly.
9 cups Rice Krispies cereal
Dump the mixture into the prepared pan and press it down very gently, with a light hand, into an even layer. Use wax paper or lightly spray your clean hands with nonstick cooking spray. Don't press too hard or your trees will end up tough and dry.
Allow the Rice Krispies to set slightly and cool, at room temperature, for 20 minutes.
Lift the treats out of the pan, use a sharp knife to cut into two long rectangles first, and then slice each rectangle diagonally (6 triangles per rectangle shape) to form a tree/triangle shape.
Melt the white chocolate chips or candy melts in the microwave, in 20-second bursts, stirring well after each one until melted and completely smooth. Transfer the melted chocolate into a piping bag or Ziplock bag with a tiny corner snipped off. Pipe the tree garland across each Christmas tree.
1 cup white chocolate chips OR white melting wafers
While the chocolate is still wet, place a star at the top of each tree, and add mini M&M's as ornaments to decorate the trees.
mini m&m's, star-shaped sprinkles
Let the chocolate set and harden completely before serving or storing. Enjoy!