In a large bowl, cream the butter and sugar together until light and fluffy.
Add eggs to the batter mixing in one at a time until incorporated. Next, add in half the flour, then half the milk, and repeat until all combined.
Divide the batter in half and pour 1/2 into a piping bag and then add cocoa to the 2nd half.
Pipe the cake batters into the bundt pan alternating colors and spreading the batter up the sides. Top with remaining batter and swirl before baking at 350F for 65 minutes..
Allow cake to cool completely before adding glaze.