<section class = "menu">
<?php

// function display_menu()
// {

     $menu = Array(
                "1" => Array (
                                "title" => 'Add task',
                                "page"  => 'add_task',
                                "url"   => "add_task.php",
                                'children' => Array()
                                        ),
                "2" => Array (
                                "title" => "Today",
                                "page"  => 'today',
                                "url"   => "main_page.php",
                                'children' => Array()
                                        ),
                "3" => Array (
                                "title" => 'Week',
                                "page"  => 'week',
                                "url"   => "" ,
                                'children' => Array()
                                        ),
                "4" => Array (
                                "title" => 'Show all',
                                "page"  => 'show all',
                                "url" => "",
                                "children" => Array(
                                            "1" =>
                                                Array (
                                                    'title' => 'Categories',
                                                    'url' => 'index.php',
                                                    'children' => Array(

                                                    "1" =>
                                                        Array (
                                                            'title' => 'Work',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),

                                                    "2" =>
                                                        Array (
                                                            'title' => 'House',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),
                                                    "3" =>
                                                        Array (
                                                            'title' => 'Education',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),
                                                    "4" =>
                                                        Array (
                                                            'title' => 'Entertainment',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),
                                                    "5" =>
                                                        Array (
                                                            'title' => 'Other',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),
                                                        ),
                                                ),
                                                "2" => Array (
                                                    'title' => 'Frequently used tags',
                                                    'url' => 'index.php',
                                                    'children' => Array(
                                                    "1" =>
                                                        Array (
                                                            'title' => 'Work',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),

                                                    "2" =>
                                                        Array (
                                                            'title' => 'House',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),
                                                    "3" =>
                                                        Array (
                                                            'title' => 'Education',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),
                                                    "4" =>
                                                        Array (
                                                            'title' => 'Entertainment',
                                                            'url' => 'index.php',
                                                            'children' => Array(),
                                                            ),
                                                            ),
                                                            ),
                                                            ),
                                                            ),



                "5" => Array (
                                "title" => 'Tags',
                                "page"  => 'tags',
                                "url"   => ""
                                        ),
                "6" => Array (
                            "title" => 'Settings',
                            "page"  => 'settings',
                            "url"   => ""
                                    ),
                "7" => Array (
                            "title" => 'About us',
                            "page"  => 'about',
                            "url"   => "about.php"
                                    )

        );
         function buildMenu($makemenu)
 {
        echo "<nav>";
        echo "<ul>";
        //echo count($menu);
        for ($i = 1; $i <= count($makemenu); $i++)
        {
                echo '<li><a href= ' . $makemenu[$i]['url'] . '>' . $makemenu[$i]['title'] .'</a>';
                 if ( ! empty($makemenu[$i]['children'])) {
                    echo "<ul>";
                    buildMenu($makemenu[$i]['children']);
                    echo "</ul>";
                }
                 echo "</li>";
        }

        echo "</ul>";
        echo "</nav>";

}
echo buildMenu($menu);

//}

?>

</section>