The family tree diagram provides a graphical view of a subset of a contact's relationships. Parent, child and spouse contacts are displayed in a hierarchical form, with right-angled connectors:
You can configure the set of relationships shown on the diagram via the CRM tab of The Practice, as well as toggling them individually on the diagram itself.
As with the contact relationship diagram, you can interactively add contacts to the diagram (by creating new contacts or forging new relationships with existing contacts). ContactsLaw will make some assumptions about how new contacts fit into the existing diagram (e.g. adding a child to a contact with a spouse will optionally add the child to the spouse contact as well).