Crush the Oreos in a food processor, processing until they are fine crumbs.
Melt butter and mix with the cookie crumbs. Press the cookie crumb mixture into a 7 inch spring form pan, covering the bottom.
Put the prepared pan into the freezer while you make the filling.
Cheesecake Filling
In a mixture beat the cream cheese until it is smooth.
Add the sugar and mix until combined. Then add the eggs one at a time, mixing well and scraping the bowl in between each addition.
Add the cocoa, buttermilk, vinegar and vanilla and mix until well combined. Stir in food coloring and mix well. Pour on top of the prepared crust.
Pour 1 1/2 cups of water into the bottom of the Instant Pot, then add the trivet to the pot.
Cover the spring form pan with foil. Then fold a long piece of foil lengthwise to make a sling that can be used to take the cheesecake in and out of the Instant Pot.
Place the sling under the cheesecake pan and lower it onto the trivet.
Put the lid on the instant pot and lock in place. Set the pot on Manual and cook the cheesecake at high pressure for 40 minutes.
Once the Instant Pot beeps let it release pressure naturally for 10 minutes, then quickly release the rest of the pressure.
Take the lid off and use the foil sling to carefully lift the cheesecake out of the Instant Pot. Take the foil off the top and let the cheesecake cool to room temperature.
Refrigerate the cheesecake, still in the spring form pan. Remove the spring form pan after the cheesecake has been refrigerated for a few hours.
Topping
After the cheesecake has been refrigerated for 8 hours or overnight make the topping and decorate the cheesecake.
Beat the cream cheese until smooth.
Add the sugar and mix until combined. then mix in the cream and beat until soft and fluffy.
Spread the topping over the cheesecake, to the edges. Then fill a pastry bag and pipe topping around the edge of the cake. Finish by decorating with colored candies.