The plugin looks up the sub-attributes in your product, then for each value it looks up its parent and adds the parent attribute and the parent value in the product.
When using a filter with the main attribute on the store page, all the products that have that main attribute are returned, which are the same products that contain the associated sub-attributes.
Important:
You can’t create multiple hierarchy levels, just one.
Two diferent attributes cannot contain the same sub-attribute.
Documentation
vitt attribute hierarcht for woocommerce
