Attributes

Hello
First of all, thank you for this awesome plugin!

I’m making a car dealer classifieds website, so I need to have the car brand and model selector.
Because I need that selector on the listings creator page, I can´t use another plugin to have that, so I was trying to make myself all the brands and models in the attributes page but is not working.
If I make an attribute (ex: Toyota), and then I make a model (ex: Supra) then i Use Toyota as a (parent), on the selector appear both and not like a submenu.

Is there a way to make this?
A car brand and model selector would be a very nice feature or add on for those who are making a car dealer listings website with this plugin.

I really need some help
Thanks in advance