PROD-I-757 Custom Fields- Sub dropdown option - Microland

Hi Team, This is a request from my client Microland, where they are looking for options to have a sub-dropdown added to the custom fields (Drop down Type). Below is the text from the client sent email for reference; "For example, the first custom field containing options as mentioned in the image below: Refer image 1 Now, under the field support functions, we would want to have a sub drop down with options as mentioned in the image below: Refer image 2 Similarly, we would like to have a sub-drop down list for all of the fields in the main drop down."