about treelist select command

[Teoman]

Hi,
I have treelist.it has nodes.when i click to expand the treelist it behaves i selected it.but i dont click select button i only click the + icon on treelist.this is the code which i tried.

    protected void RadTreeList1_ItemCommand(object sender, TreeListCommandEventArgs e)
    {
        if (e.CommandName == RadTreeList.SelectCommandName)
        {
            TreeListDataItem item = e.Item as TreeListDataItem;
            Guid depid = new Guid(item.GetDataKeyValue("DEPID").ToString());
            RadWindow1.VisibleOnPageLoad = true;
            RadWindow1.NavigateUrl = "department-update.aspx?depid=" + depid;
        }
    }

and this is my button

<telerik:TreeListButtonColumn ButtonType="ImageButton" CommandName="Select" ImageUrl="Contents/Icons/select.png"
                    UniqueName="Select">