SPList supervisorList = web.Lists["SupervisorList"];
if(supervisorList !=null)
{
ddlSupervisor.Items.Clear();
foreach (SPListItem items in supervisorList.Items)
{
string supervisorName = items["SupervisorName"].ToString();
ddlSupervisor.Items.Add(supervisorName);
}
ddlSupervisor.DataBind();
}