In Product UI multiple product categories could be assigned, and one of them is marked as base category.

The category assignment could be found in table below with product guid specified:

However, there is no indicator in that table for base category. Instead, it is calculated by the method below:

A category is regarded as base category if it belongs to the product base hierarchy. The base hierarchy is determined by the combination of application type and product type.

You can assign hierarchy to application in the customizing below: