Try like this:
public SelectList GetAllprofsssinList()
{
var PList = new List<professional();>
ds = dropdown.GetDropDownList();
List<SelectListItem> lstProfessional = new List<SelectListItem>();
for (int record = 0; record <= ds.Tables[1].Rows.Count - 1; record++)
{
dynamic row = ds.Tables[1].Rows[record];
lstProfessional.Add(
new SelectListItem
{
Text = Convert.ToString(row["ID"]),
Value = Convert.ToString(row[DescriptionName]
});
}
SelectList testList = new SelectList(lstProfessional);
return testList;
}