how to one checkboxlist multiple items to bind another checkboxlist in asp.net

<asp:CheckBoxList ID="main_check" runat="server" AppendDataBoundItems="true"
                                RepeatColumns="5" RepeatDirection="Horizontal" AutoPostBack="true"
                                onselectedindexchanged="main_check_SelectedIndexChanged" />

<asp:CheckBoxList ID="sub_check" runat="server" AppendDataBoundItems="true"
                                RepeatColumns="10" RepeatDirection="Horizontal" />

protected void main_check_SelectedIndexChanged(object sender, EventArgs e)
    {

        foreach (ListItem li in main_check.Items)
        {
            if (li.Selected)
            {
                sbp.busines_id = Convert.ToInt16(li.Value);
            }
        }
        sbp.tag = 3;   
            sub_check.DataSource = sbb.sub_busines_bind(sbp);
            sub_check.DataTextField = "category_name";
            sub_check.DataValueField = "sub_busines_id";
            sub_check.DataBind();
}