Shopify don’t support nested Collection, But some time you want to organize/show products in 2 or more level of categories of product. We would create a sub collection using product tag and need some more works to show data in sub category.
Define your categories and subcategories
For example you want to have this hierarchy of categories/collections
Create a collection for each top category (“Pants” this case)
Assign Product tag to each product corresponds to each sub category/collection. Use the category name (such as Summer, Spring) as product tag name.
Show sub category/collection in storefront
To show sub category in shop menu we will use Navigation. Create Navigation/Link lists for each top category that point to top collections. In think links lists we add link to each sub category. Sub category link is link with correspond product tag (using “Filter with tags” feature)