Add an item into combobox

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C#

Hi, i have the a combobox named cmbYear, inside the combobox have the items year eg. 2014, 2013, etc. The items are bind through data source as below:

<dx:ASPxComboBox ID="cmbYear" runat="server" ClientIDMode="AutoID"
        DataSourceID="yearDataSource" ValueType="System.String"
        ValueField="Years" TextField="Years" SelectedIndex="-1">
       <Columns>
           <dx:ListBoxColumn Caption=" " FieldName="Years" />
       </Columns>
</dx:ASPxComboBox>
    <asp:SqlDataSource ID="yearDataSource" runat="server"
        ConnectionString="<%$ ConnectionStrings:vsCustomizationRequestConnectionString %>"
        SelectCommand="SELECT DISTINCT YEAR(CreateDate) AS Years FROM CRF_Project ORDER BY Years DESC">
    </asp:SqlDataSource>

and now i want to add a new item on TOP or in another word as the first item in the combobox and i use the following codes:

cmbYear.Items.Insert(0, new ListEditItem("Latest"," "));

if (cmbYear.SelectedItem != null)
{
    if (cmbYear.SelectedItem.Text == "Latest")
    {
        yearsStatus = DateTime.Now.ToString("yyyy");
    }
    else
    {
        yearsStatus = cmbYear.SelectedItem.Text.TrimEnd();
    }
}
else
{
    yearsStatus = DateTime.Now.ToString("yyyy"); ;
}

but when i run my program, the new item which is "Latest" cannot be displayed inside the combobox, any idea?