BigCommerce Customer Groups API - How to tell if category type discount applies to subcategories?

Question

On the BigC dashboard, I can configure two types of discount applications to Category Level discount:

1. "products in this categories only"
2. "products in this category and its subcategories".

Example Customer Group Category Level

When retrieving the customer groups via the API, how can I tell which way it was configured? The API returns back very limited information pertaining to customer groups. For example:

[
  {
    "id": 1,
    "name": "Sample Customer Group",
    "is_default": false,
    "category_access": {
      "type": "all"
    },
    "discount_rules": [
      {
        "type": "category",
        "category_id": "20",
        "method": "fixed",
        "amount": "9.0000"
      },
      {
        "type": "category",
        "category_id": "3",
        "method": "percent",
        "amount": "10.0000"
      }
    ]
  }
]

I can see the category it applies to, and the level of the discount, but the API doesn't return back whether the discount applies to just the category, or also it's subcategories. How can I get this info?