About Custom Subselection

Hi all, I have a question related to the subselection of mutation.
Normally, the subselection is sin scalar type or defined Type on Schema. But in case I need a custom Type, how can I define a custom Subselection?
For example my query is:

MATCH (c:Company {id:1}) RETURN c.name as name, size((c)-[]-(:Employee)) as total_employee

So in this case, I need a subselection type with 2 elements named ‘name’ and ‘total_employee’