You can use Pocket. Just select the top edge of your cone as the Geometry, set your pocket depth to whatever you need it to be, set your offsets in the Technology page then go to Advanced just under the Technology tab. In here click on wall draft angle and fill the boxes to what ever you need, in your case the External Wall Angle should be set to 10.
This technique works for Pocket & Profile milling and I find it a really handy feature. My only dislike is that you can't do a helical toolpath in Profile milling to reduce air moves when feeding to the next level so when I want to get a really good surface finish I'll leave a little material on the walls then go over them with an HSM spiral finish op.
Hope that helps.