Dynamically add items to rad multiselect combobox on selection of particular item inside combobox

[Joe]

Hello,

I have multi select combo box which shows countries. I want to show states of countries in that same drop down only if that country is selected. See example below. Only if USA is selected in the multi select drop down, then only show states under USA as multi select drop down. Likewise for other countries in the drop down too. Is this something achievable?

USA

USA-Arizona

USA-California

USA-Texas

MEXICO

Mexico-Tijuana

Mexico-Hidalfgo

[Attila Antal]

Hi Joe. 

To be able to give you an accurate answer, I would need to know if you are referring to RadComboBox with Multi Columns, RadMultiColumnComboBox, or RadMultiSelect? 

Also, could you share the current implementation you have (markup code from the ASPX page, related JavaScript, and C#/VB code)?