Defining Hierarchies among Custom Record Values
A custom record type can be set up to permit users to define hierarchies among values for that custom record type. Note that this hierarchy is not for the relationships between various custom record types, but rather for the relationships between instances of the same custom record type.
For example, a custom record type has been created to store employee information. You can set up hierarchies between instances of this record type to indicate supervisory relationships.
First the custom record type must be set up with the Hierarchy option enabled.

When the hierarchy functionality is enabled on the custom record type definition page, you can define a parent-child hierarchy between two record instances of the same type. This hierarchy can be defined either on the parent record or on the child records.
On a parent record instance, you can click New Custom Employee on the Child Records subtab to create a child record.

On a child record instance, you can select the parent record from the list, or create a new record instance to be the parent.

The Custom Record List page shows the hierarchy for the records in the format <parent record>:<child record>.

Although this example illustrates only two levels of hierarchy, this feature supports multiple levels of hierarchy among custom record instances.