how to bind multi select dropdown values to another drop down list

in asp.net web application I am using a list box for multi select drop down , suppose I am binding 50 items to that drop down from database ,I am selecting 5 items from that multi select drop down , how I can bind that 5 selected values with their IDs to another drop down list there only one can select and wants to save to database. anyone if can help me please post the solution code as soon as possible.