WordPress Subcategory Creates 2 urls for same page (serious issue)

I have a Big Confusion about this topic ,and its made me a bad situation and headache , someone please clear this for me .

I have this situation on wocommerce ( not really different from WordPress post structure )

If i Have a product in Category-A and Subcategory-B we have tow form of URL's :

First Form is : site-address/shop/Category-A/Subcategory-B

And second form is : site-address/shop/Subcategory-B

now here is my confusion : Is this a real duplication and is it really bad for SEO or this is just a myth ? Is Search engine crawler really find the second form of the URL if i never mention this url in my web site ?

If this is bad for SEO , should i prevent use subcategories at all , if i don't want to use custom codes in my wordpress site ?

any help will be appreciated , thanks in adavance

This can get a bit demanding to get it right so this following snippet should provide the basic upon which you can research and build a more complete solution:

add_action( 'template_redirect', function() {
    if ( is_category() ) {      
        $term = get_queried_object();

        if ( isset( $term->parent ) && $term->parent ) {
            global $wp;

            $request_url = trailingslashit( get_site_url( get_current_blog_id(), $wp->request ) );
            $link = get_term_link( $term );

            if ( ! is_wp_error( $link ) ) {
                if ( strpos( $request_url, trailingslashit( $link ) ) !== 0 ) {
                    wp_safe_redirect( $link, 301 ); 
                }                   
            }
        }
    }
} );

This solution will work with pagination too but it will redirect to the start of pagination in case you are attempting to access an "incorrect" sub-category paged URL (http://www.example.com/category/child/page/2/ will redirect to http://www.example.com/category/parent/child/ -- this can be addressed by checking if we have a paginated request and build the redirect link accordingly)