How To Generate Multiple DropDownLists

I have to generate multiple dropdownlists on clientclick. That is new dropdownlists on every client click.
I placed a button and wrote code on click event. protected void addReq1_Click(object sender, ImageClickEventArgs e)

{
DropDownList oDdl = new DropDownList();
oDdl.ID = "ddlReq" + (++i).ToString();
oDdl.DataSourceID = "DSUsers";
oDdl.DataTextField = "UName";
oDdl.DataValueField = "UName";
HtmlTableCell tc0 = new HtmlTableCell();
HtmlTableCell tc1 = new HtmlTableCell();
HtmlTableCell tc2 = new HtmlTableCell();
HtmlTableCell tc3 = new HtmlTableCell();
tc2.Controls.Add(oDdl);
HtmlTableRow tr = new HtmlTableRow();
tr.Cells.Add(tc0);
tr.Cells.Add(tc1);
tr.Cells.Add(tc2);
tr.Cells.Add(tc3);
search2.Rows.Add(tr);
}

Here "DSUsers" is SqlDataSource. "i" is static variable. "serarch2" is html table with runat server tag The problem is only one control is getting rendred, after that on every additional click same DropDownList is getting replaced. No new DropDownList is added to the page.