Handling Dropdown conditional Dropdowns

I'm working on a material design web-app designed for a mobile/touch environment.

Obviously I have tight space constrains and would like to know what is the best-practice for conditionally providing a sub-set of options.

I don't really like the idea of showing two selects only when the appropriate option is selected.

Example:

  • Option 01
  • Option 02
  • Option 03
  • Option 04
  • Option 05 (only this has the "sub-options" i.e. [sub1, sub2, sub3, sub4, sub5])

example dropdown

More info about the context: these are a sort of preferences... options in this case are different kinds of visualizations but the option number five has a more detailed visualization divided by areas.

(Thanks @cyberspark I don't know how to thank you for edit)

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