If you don't have grandchildren, and you don't have grandparents, then all you really have is a parent and a child. In those cases it seems all you need are two pointers, one for for the parent and one for the child. Then the index would look like this and require 2 tables a parent (with parent keys) and a child, with a parent and child key for each record:
... child table
PARENT1.CHILD1
PARENT1.CHILD2
PARENT1.CHILD3
PARENT2.CHILD1
PARENT3.CHILD1
PARENT3.CHILD2
.. so on -

>Nah. I thought I was being more economical by having my key structures like this: