Auto refresh the drop-down

I have an option in dropdown like "Add new option" written using grouped_collection_select.

And when user clicks on the "Add new option". A pop up dialog appears to add a new value. And when I click create it hits the database and adds the value to the db.

But It never updates the dropdown list. Suggest me a way to auto refresh only the current dropdown with the new vales in db when a new value is added.

What I like to do in this case is to use JavaScript to replace the select with a text field. Anything entered into the text field (which picks up the same name as the select it replaces) gets added to the collection, and once the form is submitted, the select gains that new value, sorted into alphabetical (or whatever) order. I have a function that does all this automatically to any select with the classname 'combo' added to it. The Add new… option is appended to the bottom of the select, choosing it makes the select disappear, replaced with a text field. Blurring out of the text field without entering anything replaces it with the original select.