Remove selected item from DropDownList on Button click in ASP.Net

I have bound DropDownList from DataBase. When CheckBox is checked then Selected Value of DropDownList will be deleted.

HTML:

<form id="form2" runat="server">
<div>
    <asp:DropDownList ID="ddlCity" runat="server">
    </asp:DropDownList>
    <br />
    <asp:CheckBox ID="chkDelete" Text="Delete" runat="server" />
    <br />
    <asp:Button ID="btnUpdate" runat="server" OnClick="Delete" Text="Delete" />
</div>
</form>

C#:

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.GetCities();
    }
}

private void DeleteSelected(string city)
{
    // fire your delete query;
    this.GetCities();
}

protected void Delete(object sender, EventArgs e)
{
    if (this.chkDelete.Checked)
    {
        this.DeleteSelected(this.ddlCity.SelectedItem.Text);
    }
}

private void GetCities()
{
    string constr = ConfigurationManager.ConnectionStrings["ConString2"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT DISTINCT (City) FROM City", con))
        {
            using (SqlDataAdapter da = new SqlDataAdapter(cmd))
            {
                con.Open();
                DataSet ds = new DataSet();
                da.Fill(ds);
                this.ddlCity.DataTextField = "City";
                this.ddlCity.DataValueField = "City";
                this.ddlCity.DataSource = ds;
                this.ddlCity.DataBind();

            }
        }
    }
}

Thank You.