Problem update panel event fires twice

Question

here update panel event fires twice as i clicked on button
and record inserted twice why it is happening donno
 
please help 
 

 

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<asp:UpdatePanel ID="upanelfolder" runat="server" UpdateMode="Conditional"> <ContentTemplate><asp:Label ID="Label1" runat="server" Text= <%=prod_name %>
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</ContentTemplate> <Triggers> <asp:AsyncPostBackTrigger ControlID="btn" EventName="Click" /> </Triggers> </asp:UpdatePanel> 

<asp:Button ID="btn" runat="server" OnClick="btn_Click" Text="Add" />
 
code behind
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Protected Sub btn_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btn.Click //insert query End Sub