2 level field entry to avoid a big list of options in the pull down menu

2 level field entry to avoid a big list of options in the pull down menu

I want a section in the New Leads tab to go something like this and avoid a huge number of options to choose from:

Lead source
- direct marketing (then have a pull down that says cold call, advertisement, email)
- broker (then have a pull down that says individual broker, group, boutique bank)
- industry (then have a pull down that says conference, tradeshow, magazine)

My goal is to avoid a single pull down with 50 options, which given the # of lead sources I have (7) and the options per lead source (5-8) is about what I would have.

How can I do this?