new SelectList(_context.Set razor code example

Example: class selector to property in asp net core dropdown

<select data-val="true" data-val-required="The Employee field is required." id="Employee" name="Employee">    <option value=""></option>    <optgroup label="IT">        <option value="1">Mike</option>    </optgroup>    <optgroup label="Sales">        <option value="2">Pete</option>        <option value="4">Dean</option>    </optgroup>    <optgroup label="Admin">        <option value="3">Katy</option>    </optgroup></select>