Filter child CheckBoxList Items based on parent CheckBoxList selection in ASP.Net

Refer:

1. Filter ASP.Net GridView data based on CheckBoxList Checked Items

Please consider the above example and based on the CheckBox1 List Selection bind CheckBoxList2.

HTML

<asp:CheckBoxList ID="chkCountries" runat="server" AutoPostBack="true" OnSelectedIndexChanged="Country_Selected">
    <asp:ListItem Text="Argentina" Value="Argentina"></asp:ListItem>
    <asp:ListItem Text="Austria" Value="Austria"></asp:ListItem>
    <asp:ListItem Text="Belgium" Value="Belgium"></asp:ListItem>
    <asp:ListItem Text="Brazil" Value="Brazil"></asp:ListItem>
    <asp:ListItem Text="Canada" Value="Canada"></asp:ListItem>
</asp:CheckBoxList>
<br />
<hr />
<br />
<asp:CheckBoxList ID="CheckBoxList1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="Country_Selected">
</asp:CheckBoxList>

C#

protected void Country_Selected(object sender, EventArgs e)
{
    this.BindCheckBoxList();
}

private void BindCheckBoxList()
{
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    string query = "SELECT * FROM Customers";

    string condition = string.Empty;
    foreach (ListItem item in chkCountries.Items)
    {
        condition += item.Selected ? string.Format("'{0}',", item.Value) : "";
    }
    if (!string.IsNullOrEmpty(condition))
    {
        condition = string.Format(" where Country in ({0})", condition.Substring(0, condition.Length - 1));
    }
    SqlCommand cmd = new SqlCommand(query + condition);
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            cmd.Connection = con;

            sda.SelectCommand = cmd;
            using (DataSet ds = new DataSet())
            {
                sda.Fill(ds);
                CheckBoxList1.DataTextField = "ContactName";
                CheckBoxList1.DataValueField = "CustomerId";
                CheckBoxList1.DataSource = ds;
                CheckBoxList1.DataBind();
            }
        }
    }
}

Screenshot