Here's how we can set this up in CRM.
Use the Product Category or Unit field (or create a custom field) to distinguish between single products and product groups
Create a Custom Module with two Product Lookup fields (and any other fields you may need):
- Product Group (Related List name: Group Members)
- Group Member (Related List name: Product Groups)
To add a product to a product group, create a record in the custom module - select the Product Group in the Product Group lookup field and select the individual product in the Group member field.
When you view the Product Group, you'll see the list of Products in the Group - something like this: