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.

Andrei Zobnin

This plugin returns the option to choose a product attribute type, which was removed from WooCommerce 3.3. With this plugin you can use select/text/number/textarea type.
WooCommerce requires at least: 3.6

Text Attributes for WooCommerce

Allows you to type attribute values in the input field instead of choosing from the drop-down list.

Vitt Attribute Hierarchy for WooCommerce vs Text Attributes for WooCommerce