I am trying to create a database to help with my family's grocery shopping list maintenance. The database I have set up has the following tables established


Categories (For different food categories)
Items (For list of items that will be purchased)
Lists (To hold the current list for each store)
Size Categories (To determine the size of the items)
Stores (To contain information about each store Address, City, etc.)

The structure of the Categories table is as follows:
Field1: ID (Contains an autonumber field that is the primary key)
Field2: CategoryName (Contains the text that describes the category i.e. Produce, meats, etc)
Field3: ParentCategory (Contains a lookup to the CategoryID field to allow nesting of one category into another)

The structure of the Items table is as follows:
Field1: ID (Contains an autonumber field that is the primary key)
Field2: Item (Text field containing the name of the item. i.e. Carrots, white bread, etc)
FIeld3: SizeCategoryID (Lookup into the Size Category table to determine category of size used for a particular item)
Field4: Size (Contains a numeric value for the size So if the category is fluid ounces this field will hold the number of fluid ounces in the container)
Field5: StoreID (Contains the lookup to the store ID for which store the intended item will be purchased at.)
Field6: Price (Contains a currency value for price of the item at the selected store.)

The structure of the SizeCategories Table is as follows:
Field1: ID (Autonumber field that is the primary key)
Field2: SizeCategory (Text field containing the size category description i.e. Fluid ounces, dry weight, Ounces, pounds, etc.)
Field3: Parent Category (Lookup to the ID field to allow subcategories for size To have multiple layers)

The structure of the Store Table is as follows:
Field1: ID (Autonumber field that is the primary key)
Field2: StoreName Contains the stores name
Field3: Address1 (Contains the first address line for store)
Field4: Address2 (Contains the second address line for the store)
Field5: City (Contains the city the store is located in)
Field6: State (Lookup to state table that contains State names and postal abbreviations for sall 50 states)
Field7: Zip (Zipcode for store)

My question is mostly related to how to create the forms comboboxes in the Category and SizeCategory form fields so that in the form a user can create a new category and place it in another category from the form. As an example if the user creates the category meats using the form and then creates the category chicken how do I allow them to create its parent category as meats and to take it one step further if the user creates a category frozen and then creates a sub category of meats and wants to create a sub-sub category under frozen-Meats and call it chicken so that the category for Frozen Chicken breasts would be found under the category Frozen-Meats-Chicken how do I go about creating this combobox to allow such a selection? I am using Access 2013 if that makes any difference.