How do i use a dropdown menu to give the user certain options based on that first dropdown?

[Tiger1]

I have a drop down menu. I want the user to first choose from that drop down menu. Once they choose from that - i want to only give them options based on that value:
For example, if the user has a choice:

Enum:
Item A
Item B
Item C

If the user chooses “Item A” - then they can choose from another drop Down:
Item aa
Item aaa
Item aaaa

If the user chooses “Item B” - they can choose from these options:
Item bb
Item bbb
Item bbbb

etc…

Item