title: How to add an additional RadComboBoxItem to data bound RadComboBox?
body: <p>I am using Telerik controls on my aspx page. I have cascading radcombo boxes(dropdown box). I have 3 of them on my page. the values of 2nd rad combo box depends on the 1st and the 3rd depends on selection of 2nd. The thing is that i want to include a select all option in the 3rd dropdown. The values are coming from a database i.e all of them are data bound. How can i add a 'select all' option in the combo boxes? i tried it using parameters.insert function in c#, but does not work. i tried adding in the control itself but not showing up with that either. </p>
  
  <p>Can someone please help?</p>