multi-level select filter with dropdowns for each level 1 value

I would like to create a filter module where a multi-level select is presented as seperate dropdowns for each level1 value with the values in the dropdown being all the values under each level1. Level 2, 3, and further could also be in the dropdown but indented with "--" for each level.

For example:

A - AA - AAA
A - AA - BBB
A - BB - AAA
A - BB - DDD
B - CC - EEE
B - CC - FFF

Dropdown 1:

A
--AA
----AAA
----BBB
--BB
----AAA
----DDD

Dropdown 2:

B
--CC
----EEE
----FFF

Any suggestions on the most efficient way to approach this? Is there anything in the API that I could utilize to retrieve the field values or should I just do that via SQL?