Admin Order City dropdown based on state

I am trying to add a city dropdown in my Woocommerce store’s admin order edit area. I have tried this code.

I have added places as an array. And here is the full code in Github.

global $places;
$places['BD'] = array(
    'dhaka' => array(
        __('Aam Bagan', 'woocommerce'),
        __('12 Tala', 'woocommerce'),
        __('Keraniganj Upazila Sadar', 'woocommerce'),
    ),
    'faridpur' => array(
        __('Alfadanga', 'woocommerce'),
    ),
    'gazipur' => array(
        __('Gazipur Sadar', 'woocommerce'),
        __('Kaliakair', 'woocommerce'),
    ),
    'gopalganj' => array(
        __('Gopalganj Sadar', 'woocommerce'),
        __('Kashiani', 'woocommerce'),
    ),
    'jamalpur' => array(
        __('Bakshiganj', 'woocommerce'),
        __('Dewanganj', 'woocommerce'),
    ),
);

function enqueue_scripts()
{
    wp_enqueue_script('jquery');
    wp_enqueue_script('select2', 'https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.13/js/select2.min.js', array('jquery'), '4.0.13', true);
    wp_enqueue_script('place-select-js', plugin_dir_url(__FILE__) . 'js/place-select.js', array('jquery', 'select2'), '0.1', true);
}
add_action('admin_enqueue_scripts', 'enqueue_scripts');


add_filter('woocommerce_admin_billing_fields', 'admin_billing_city_select_field');
function admin_billing_city_select_field($fields)
{
    global $pagenow, $places;

    // Only for new order creation
    if ($pagenow != 'post-new.php') return $fields;

    $options = array('' => __('Select a city…', 'woocommerce'));
    if (isset($places)) {
        foreach ($places as $state => $cities) {
            foreach ($cities as $city => $city_name) {
                $options[$city] = $city_name[0];
            }
        }
    }

    $fields['city'] = array(
        'label'   => __('City', 'woocommerce'),
        'show'    => false,
        'class'   => 'js_field-city select short',
        'type'    => 'select',
        'options' => $options,
    );
    return $fields;
}

Here in Admin pannel it’s returning only the first item from the Array list of places. I I chage the $options[$city] = $city_name[0]; to $options[$city] = $city_name; it’s giving a String “Array”

How can I show all the city name based on state?

The page I need help with: [log in to see the link]