Preheat the oven to 350°F. Line 24 muffin cups with paper liners.
In a large bowl, or the bowl of a stand mixer, whisk together the cocoa powder, all-purpose flour, cake flour, sugar, baking soda, baking powder, and salt until well combined.
Add the eggs, buttermilk, water, oil and vanilla and mix with an electric mixer, or stand mixer, until well combined, about 2 minutes.
Fill the cupcake liners 2/3 full and bake for 20 minutes or until a toothpick inserted in the center comes out with just a few crumbs.
Remove from the pan and cool completely on a wire rack.
For the Christmas Trees:
Place the candy melts in a bowl and melt them in the microwave at 50% power for 2-3 minutes, stirring every 30 seconds, until completely melted.
Place a ziplock bag or a piping bag in a cup to hold it and fill the bag with the melted candy.
Seal the ziplock and cut a small hole in the corner of the bag.
On a sheet of wax paper, pipe lines of candy, about 2/3 the length of a pretzel stick and press the pretzel into the candy. Then pipe lines back and forth across the pretzel to make a tree shape.
Top with sprinkles for ornaments.
Repeat for the remaining trees and then let the candy set completely before carefully removing the trees from the wax paper and placing them on the cupcakes. It takes 1-2 hours for the candy to set completely.
For the Frosting:
With an electric mixer, or in the bowl of a stand mixer, cream the butter until it is smooth and creamy, about 2 minutes.
Add the powdered sugar and heavy cream and beat for a full 3 minutes until it is light and fluffy. Add a little more sugar if it’s too runny or a little more cream if it’s too thick.
When the cupcakes are completely cool, decorate them by spreading a layer of frosting on top with a knife.
Sprinkle the frosting with shredded coconut, or dip the cupcake into the coconut to cover it, and carefully place three Christmas trees on top of each cupcake.