product_type is your own category for each product. Google uses it to understand the catalog and you use it to split Shopping campaigns. Most stores already have it - as a path like Home > Garden > Pots.
- Open the data source, go to Rules and click Add rule - for example “Product type from category”.
- Under Then pick product_type and choose Split text.
- Set Take from to your category field and Split on to the separator, for example
>(with the spaces). - Choose the parts: Start at part
1with Start counted from Beginning, and End at part1with End counted from End, keeps the whole path;1from the End for both keeps only the last level. - Set Join with (optional) - for example
>again - check Preview changes and Save rule.

Example

categoryShoes > Men > Running, positions 1 from the Beginning to 1 from the End →Shoes > Men > Running- Positions 1 from the End to 1 from the End →
Running - Positions 1 to 2 from the Beginning →
Shoes > Men- the rule in the pictures
Positions are counted from 1. For Google's own taxonomy use Assign Google product categories.