Whisk your wet cake ingredients together - oil, water, eggs, and Greek yogurt
Add your cake mix and protein powder and mix with a wooden spoon until fully combined
Pour into greased 9x13 cake pan and bake for 25-28 minutes
Allow to cool completely
Invert the cake onto a cutting board, and slice the cake in half horizontally to thin out your trees
Use a Christmas tree cutter to cut cake trees out - I got 22
Use your hand or standing mixer to combine buttercream ingredients until whipped, several minutes
Place buttercream on half of your trees, then top with remaining tree brownies
Melt your dark chocolate and coconut oil in 30 second intervals until smooth
Dip each stuffed brownie into melted dark chocolate, then onto parchment paper, and to the fridge for chocolate and filling to fully set, about 30 minutes
Decorate with melted white chocolate, dye-free sprinkles, and enjoy!