thevittfile

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.
<h3>Documentation</h3>
<a href="https://github.com/vittfiles/vitt-attribute-hierarchy" rel="nofollow ugc">vitt attribute hierarcht for woocommerce</a>

Vitt Attribute Hierarchy for WooCommerce

This plugin works simulating a hierarchy for attributes and subattributes.

Restores WordPress default functionality prior to version 4.7 where image ALT attributes were automatically generated and put into the HTML code. The ALT attributes were generated from the Caption (if it exists) else from the Title (if it exists) of the image in the Media Library. This plugin utilises Titles in generating ALT text, but does not utilise Captions. The Title used by this plugin, is the main Title of the image as found in the Media Library, not the HTML TITLE attribute of the image (that is something else, which this plugin ignores).

Automatic image ALT attributes

This feature is a time saver for me as my site is image oriented.

Thanks

Automatically generates ALT attributes in image HTML. Restoring WordPress < 4.7 functionality.

Vitt Attribute Hierarchy for WooCommerce vs Automatic image ALT attributes