I've more than 450+ WooCommerce product categories and subcategories. I want to add them all in the menu items, categories as a top level menu and subcategories as submenu. Is there any way to automate the process?
For menus this large, it's usually more efficient to use functions like
wp_list_categories() (which can also output custom taxonomies like Product Categories) in whatever theme template you need to affect. Bonus: your menu will always be current, because unlike a static WP Nav Menu, this will always pull all Product Categories and not need manual updating.
Keep in mind, it's not always a good user experience to have such massive menus to drill down through, and Google specifically recommends having less than 100 links per page - which includes all links, not just menus. So, you may be better off just listing top-level categories in your menu, and making sure you have a robust search feature, to help with SEO and UX.