2nd Dropdownlist Depend On The 1st Dropdown List?

i want to create a dropdown list which depend on each other. as example. the 1st dropdown list will let the user to select the type between sector or subsector.

select type: 1) sector
2) subsector

if the user choose sector, the sector value will be appear in the dropdownlist

select sector: 1)technology
2) trading
3) industrial

but if the user choose subsector, the subsector value will be appear in the dropdownlist

select subsector: 1) computer
2) utilities
3) consumer

i try to use the hide code but it turns out to be error. i think because of the data overloading.