Handling of Topic Drill Downs in Databases
It looks like you're wanting to store a tree structure. This is a bit awkward with databases, but it's definitely possible. Here's a link which explains how: http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/ The "Nested Set Model" part is what you're looking for.

Applying that model to your scenario, you would get a table that looks something like this:


And a conceptual model for the first 3 levels that looks something like this (please excuse my MS Paint drawing skills): 
Obviously you would have more nodes, but it's the basic idea.