Prepare a baking sheet by lining it with parchment paper.
In a microwave-safe bowl, combine the semi-sweet chocolate chips and coconut oil. Heat in the microwave in 30-second increments until melted and smooth, stirring after each interval.
If desired, add a few drops of green food coloring to the melted chocolate and mix well until you achieve the desired shade.
Dip one end of each marshmallow into the melted chocolate, allowing any excess to drip off. Place the dipped marshmallow, chocolate-side down, onto the prepared baking sheet.
Once all marshmallows are positioned on the baking sheet, use a piping bag or resealable plastic bag to pipe melted chocolate from the top of the marshmallow down to form 'branches' of the Christmas tree.
Immediately sprinkle the crushed peppermint candies over the chocolate while it is still warm, allowing them to stick.
Take a wafer cookie and insert it into the bottom of each marshmallow tree as a base.
Lastly, push a mini candy cane into the top of each marshmallow to resemble a tree topper.
Allow the chocolate to set at room temperature or refrigerate for about 10 minutes to harden completely.