multiplke choice input bootstrap code example

Example: cant pass multipule select input bootstrap

<div class="col-9">
                                <select id="generals" name="generals" class="form-control kt-selectpicker"  multiple title="Choose one of the following...">
                                <optgroup label="Passport">
                                    <option value="passport_number">Number</option>
                                    <option value="passport_date">Date of issuance</option>
                                    <option value="passport_expired">Date of expiry</option>
                                    <option value="passport_office">Issuing Office</option>
                                </optgroup>
                                    <optgroup label="Personal">
                                        <option value="applicant_id">Applicant Id</option>
                                        <option value="first_name">First Name</option>
                                        <option value="first_name">Middle Name</option>
                                        <option value="last_name">Last Name</option>
                                        <option value="address">Address</option>
                                        <option value="crew_id">Crew Id</option>
                                        <option value="email">Email</option>
                                        <option value="mobile_number">Mobile Number</option>
                                    </optgroup>
                                </select>
                            </div>