You can build a list like this using the following Objects:
User Base
...Parent/Child Relationship
......User Base [1]
...Parent/Child Relationship [1]
......User Base [2]

You will also need the following Object Filters
Parent/Child Relationship.Rel Ordinal is 1
Parent/Child Relationship [1].Rel Ordinal is 2
Note: The relationship ordinal determines the order parents appear in on the list. There's currently not a different way to determine the order parents appear in within a flattened list.