Hierarchical Menu In Drupal

<?php

/**

 * Implements hook_menu() 

 */

function data_menu(){
    $items = array();

    $items['learning/data'] = array(
        'title' => 'Hello Data',
        'page callback' => 'hello',
        'access callback' => TRUE,
    );

    $items['learning/data/satu'] = array(
        'title' => 'Data Satu',
        'page callback' => 'hello_satu',
        'access callback' => TRUE,

    );

    $items['learning/data/dua'] = array(
        'title' => 'Data dua',
        'page callback' => 'hello_dua',
        'access callback' => TRUE,

    );

    $items['learning/data/dua/a'] = array(
        'title' => 'Data A',
        'page callback' => 'hello_a',
        'access callback' => TRUE,
    );
   
    return $items;


}

function hello(){
    return t('hello boo. And Hello for you all in the home of Indonesia');

}

function hello_satu(){
    return t('Holla from satu learning package in the home of you all here');
}

function hello_dua(){
    return t('Holla from all here that we can do more for this one');

}

function hello_a(){
    return t('Holla from A to Z');
}

Hierarchical Menu In Drupal