Here's how you can add your Categories and Sub categories collection to your mobile app-
Steps:
1 . Login to your Shopify Admin
2.Create a menu
- Click on Online Store
- Navigation
- Add Menu

3 . Add Menu Description
- Add a name : Mobile Categories
- Handle : mobile-categories (in small alphabets)
- Proceed to add menu items

4. Add Categories(Menu Items)
- Name the menu
- Choose the respective collection and product from Link section.
- Save

5. Create a New Menu
- Click on Online Store
- Navigation
- Proceed to add menu

6. Select the categories for which you want to add the sub-categories

Select the categories for which you want to add subcategories : ex Men's Wear
- Name : Men's Wear
- Handle: mens-wear
- Add menu item
7 . Add Link Product/Collection To Your Sub-categories
- Enter the name of sub-category
- Select the product/collection under link
- Choose the same product/collection to link
- Click on Save Menu

We hope this article is useful :)