Filter gallery to show all items of a category and all sub categories

I am trying to create an inventory app using PowerApps, currently each item falls under a main category, and at least one subcategories. A small example of this is something like this:

Concessions
|    Food
|        Chips
|            Brand 1
|            Brand 2
|            Brand 3
|        Candy
|           Chocolate
|               Brand 1
|               Brand 2
|           Hard
|           Gum
|        Grill
|    Drinks
Travel Goods
|    TravelGoodsSubCat

This is held in a google sheet (along with the inventory data in another sheet inside the same book) that looks like this:

CatID    CatName            ParentCat
1        Concessions        0
2        Travel Goods       0
3        Food               1
4        Chips              3
5        Candy              3
6        TravelGoodsSubCat  2
.... And So on....

So what I'm envisioning is two galleries, one that is horizontal across the top of the screen that shows only the categories that are a child of category 0. The second is a vertical gallery that shows every item under the current category. So if the user selects Concessions in the horizontal gallery, the vertical gallery should populate with all items assigned to categories 1, 3, 4, 5, and so on.

How do I acheive what is, in my mind, a recursive search looking for all these possible sub categories?