How to add more make and models

Hi, might sound silly but i can create make model relation. i can either create make and child of make. or models but cant relate both together. Eg: on theme demo When you select BMW it has couple of makes (x1,x2..) how to add more make under that like if you select BMW then another new model Z4 i want to add, How to do that? When I go to add more model the parent section does not show the Make.