app state and data type

I create a data type (countrystates) which

field

1. country (string)

2. State( string list)

Now I have an app state which is as follows

List<Data(countrystate)>

Now if I want to view state list based on country name

If I want to put it in drop-down. How to apply?

Please help, I haven't been able to figure it out yet.