Crea....

app/Helpers/menu_helper.php

<?php
if (!function_exists('buildMenu')) {
    function buildMenu($items, $isDropdown = false) {
        $html = $isDropdown ? '<ul class="nav-dropdown">' : '<ul class="nav-list">';
        foreach ($items as $item) {
            $hasChildren = !empty($item['children']);

            if ($hasChildren) {
                $html .= '<li>';
                $html .= '<a href="#"' . $item['title'] . '">' . esc($item['title']) . '</a>';
                $html .= buildMenu($item['children'], true);
                $html .= '</li>';
            } else {
                $html .= '<li>';
                $html .= '<a href="' . site_url($item['url']) . '">' . esc($item['title']) . '</a>';
                $html .= '</li>';
            }
        }
        $html .= '</ul>';
        return $html;
    }
}

public/assets/navigation/css/nav.css

body {
  margin: 0;
}
@charset "UTF-8";
.navigation {
  height: 70px;
  background: #212529;
}
.brand {
  position: absolute;
  padding-left: 20px;
  float: left;
  line-height: 70px;
  font-size: 1.4em;
}
.brand a,
.brand a:visited {
  color: #ffffff;
  text-decoration: none;
}
.nav-container {
  max-width: 1000px;
  margin: 0 auto;
}
nav {
  float: right;
}
nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
}
nav ul li {
  float: left;
  position: relative;
}
nav ul li a,
nav ul li a:visited {
  display: block;
  padding: 0 20px;
  line-height: 70px;
  background: #212529;
  color: #ffffff;
  text-decoration: none;
}
nav ul li a:hover,
nav ul li a:visited:hover {
  background: #2581DC;
  color: #ffffff;
}
nav ul li a:not(:only-child):after,
nav ul li a:visited:not(:only-child):after {
  padding-left: 4px;
  content: " ▾";
}
nav ul li ul li {
  min-width: 190px;
}
nav ul li ul li a {
  padding: 15px;
  line-height: 20px;
}
.nav-dropdown {
  position: absolute;
  display: none;
  z-index: 1;
  box-shadow: 0 3px 12px rgba(0, 0, 0, 0.15);
}
/* Mobile navigation */
.nav-mobile {
  display: none;
  position: absolute;
  top: 0;
  right: 0;
  background: #212529;
  height: 70px;
  width: 70px;
}
@media only screen and (max-width: 798px) {
  .nav-mobile {
    display: block;
  }
  nav {
    width: 100%;
    padding: 70px 0 15px;
  }
  nav ul {
    display: none;
  }
  nav ul li {
    float: none;
  }
  nav ul li a {
    padding: 15px;
    line-height: 20px;
  }
  nav ul li ul li a {
    padding-left: 30px;
  }
  .nav-dropdown {
    position: static;
  }
}
@media screen and (min-width: 799px) {
  .nav-list {
    display: block !important;
  }
}
#nav-toggle {
  position: absolute;
  left: 18px;
  top: 22px;
  cursor: pointer;
  padding: 10px 35px 16px 0px;
}
#nav-toggle span,
#nav-toggle span:before,
#nav-toggle span:after {
  cursor: pointer;
  border-radius: 1px;
  height: 5px;
  width: 35px;
  background: #ffffff;
  position: absolute;
  display: block;
  content: "";
  transition: all 300ms ease-in-out;
}
#nav-toggle span:before {
  top: -10px;
}
#nav-toggle span:after {
  bottom: -10px;
}
#nav-toggle.active span {
  background-color: transparent;
}
#nav-toggle.active span:before, #nav-toggle.active span:after {
  top: 0;
}
#nav-toggle.active span:before {
  transform: rotate(45deg);
}
#nav-toggle.active span:after {
  transform: rotate(-45deg);
}

Establece....

1. protected $helpers = ['menu']; en app/Controllers/BaseController.php

Configura....

app/Config/Menus.php

<?php
namespace Config;
use CodeIgniter\Config\BaseConfig;

class Menus extends BaseConfig {
    public $main_menu = [
        [
            'title' => 'Inicio',
            'url' => '/',
            'children' => [],
        ],
        [
            'title' => 'Control',
            'url' => '#',
            'children' => [
                [
                    'title' => 'Grupos',
                    'url' => 'control/grupos',
                    'children' => [],
                ],
                [
                    'title' => 'Estudiantes',
                    'url' => 'control/estudiantes',
                    'children' => [],
                ],
                [
                    'title' => 'Listas',
                    'url' => 'control/listas',
                    'children' => [],
                ],
            ],
        ],
    ];
}

Ejemplo de Vista

app/Views/layouts/main.php

<!DOCTYPE html>
<html>
<head>
    <title>Mi Aplicación</title>
    <link type="text/css" rel="stylesheet" href="<?php echo base_url() . '/assets/navigation/css/nav.css'; ?>" />
<?php
foreach ($css_files as $file): ?>
    <link type="text/css" rel="stylesheet" href="<?php echo $file; ?>" />
<?php endforeach;?>
</head>
<body>
<section class="navigation">
    <div class="nav-container">
        <div class="brand">
            <a href="<?=site_url('/')?>">Appname</a>
        </div>
        <nav>
            <div class="nav-mobile"><a id="nav-toggle" href="#!"><span></span></a></div>
                <ul class="nav-list">
<?php
$config = config('Menus');
echo buildMenu($config->main_menu);
?>
                </ul>
            </div>
        </nav>
    </div>
</section>

    <?=$this->renderSection('content');?>

    <script>
        (function($) { // Begin jQuery
          $(function() { // DOM ready
            // If a link has a dropdown, add sub menu toggle.
            $('nav ul li a:not(:only-child)').click(function(e) {
              $(this).siblings('.nav-dropdown').toggle();
              // Close one dropdown when selecting another
              $('.nav-dropdown').not($(this).siblings()).hide();
              e.stopPropagation();
            });
            // Clicking away from dropdown will remove the dropdown class
            $('html').click(function() {
              $('.nav-dropdown').hide();
            });
            // Toggle open and close nav styles on click
            $('#nav-toggle').click(function() {
              $('nav ul').slideToggle();
            });
            // Hamburger to X toggle
            $('#nav-toggle').on('click', function() {
              this.classList.toggle('active');
            });
          }); // end DOM ready
        })(jQuery); // end jQuery
    </script>
</body>
</html>

app/Views/example.php

<?=$this->extend('layouts/main');?>

<?=$this->section('content');?>

    <div style='height:20px;'></div>
    <div style="padding: 10px">
        <?php echo $output; ?>
    </div>
    <?php foreach ($js_files as $file): ?>
        <script src="<?php echo $file; ?>"></script>
    <?php endforeach;?>
<?=$this->endSection();?>