<select name="languages" id="lang" class="form-control form-control-sm">
<optgroup label="first-choice">
<option value="select">Select a language</option>
<option value="javascript">JavaScript</option>
<option value="php">PHP</option>
<option value="java">Java</option>
<option value="golang">Golang</option>
</optgroup>
<optgroup label="second-choice">
<option value="python">Python</option>
<option value="c#">C#</option>
<option value="C++">C++</option>
<option value="erlang">Erlang</option>
</optgroup>
</select>
the above code To implement this contol
<asp:DropDownList ID="ddlTicketType" runat="server" >
</asp:DropDownList>