Hello,
Yes it is not possible to handle the brands like the categories, you do not have the same module features and brands are not meant to be managed in a full tree but in just a simple list.
For sure, a custom development would be require if you want to do so ; and if you're dealing with a custom development, you can create your requirements and specifications.
A brand and a category are stored in the same database table ; they have a different "category_type" but can handle the same data. Nevertheless, they are read and processed differently in HikaShop ; which might not be the case if you're using a custom module, some custom code.
So what is your question exactly ?
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.