Is there a way to define a singleton as a list of nested types?

For example, say you have a YML which only has a list of objects at the root level (no keys, just items):

# categories.yml
- id: categoryA
 name: Category A
- id: categoryB
 name: CategoryB
- id: categoryC
 name: Category C

Doesn't look like there's a way to define that document as-is.

It's not really a big deal though, as the YML could be modified to put the list inside a named key as a workaround.

# categories.yml
categories:
 - id: categoryA
 name: Category A
 
 - id: categoryB
 name: CategoryB
 
 - id: categoryC
 name: Category C

It's possibly not be a very common use-case though.