Value Is Saved In Database But Is Not Showing In Dropdownlist

I am currently learning vb.net with sql. I have two textboxes (txtValue and txtText) , a dropdownlist (ddl1) and save button (btnAdd). I insert value to txtValue and txtText (eg: txtValue: A and txtText: Apple). When I click button Add, The value will display in dropdownlist (like this; A - Apple) and both data will be save in the sqlserver (db).

I am having issue where when i click button Add, the data is not display in the dropdownlist. But when i refresh my browser, the data will display in dropdownlist.

ASP.net

Code:
<asp:DropDownList ID="ddl1" runat="server" CssClass="form-control" AutoPostBack="true"></asp:DropDownList>
<label class="form-control-static">Value</label>
<asp:TextBox ID="txtValue" runat="server" CssClass="form-control"></asp:TextBox>
<label class="form-control-static">Text</label>
<asp:TextBox ID="txtText" runat="server" CssClass="form-control"></asp:TextBox>
<button id="btnAdd" runat="server" style="min-width: 80px;">Add</button>

VB.Net

Code:

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
If Page.IsPostBack = False Then
Dim rs As DataSet
ddl1.Items.Clear()
ddl1.Items.Add("")

[Code] .....