Tableau - turn a dimension into 2 dimensions

I have a dimension called "Category" with 4 items that we will call A,B,C & D. I am trying to create 2 separate dimensions that I can drag/drop, 1 being A,B,C and the second being D. I understand there are easy ways to filter D out but I want them to be separate dimensions. Below is what I have tried for creating the category containing only "D" but it still keeps all data of everything else but they just are just blank.

IF [D]="End-User" then [D] 
ELSE ""
END

I'm sure there is a very simple way to separate the dimension to create Category (A,B,C) & Category 2 (D) but I have tried everything that I know. Any help would be appreciated!