It is done
public Fill(List<string> contractor)
{
contractor.Sort();
comboBox1.Items.Insert(0, "All");
for (int i = 0; i < contractor.Count; i++)
{
comboBox1.Items.Add(contractor[i]);
}
comboBox1.SelectedIndex = 0;
}</string>
but I want to know that it is better than DataSource property is set.