Lightly spray a 9×13-inch pan with nonstick spray and set aside.
In a large pot over low heat, melt the butter and dissolve the salt.
Add the mini marshmallows and stir until completely melted and smooth. Remove from the heat.
Stir in the vanilla extract. Then fold in the Rice Krispies until evenly coated.
Transfer the mixture to the prepared pan. Use lightly buttered or damp hands to gently press the treats into an even layer. Don’t compact them, or the bars will turn dense.
Let cool for 1 hour. Cut the Rice Krispie treats into evenly sized triangles to create Christmas trees.
Use a little frosting to attach two leftover pieces and make one more Christmas tree.
Fill a piping bag with green frosting and use a grass tip (#233) to pipe the tree.
Add the mini M&M’s to create lights and top with a gold star.
Gently add a pretzel stick to the bottom of the treat. Enjoy!