begini lho hasilnya

<?php

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */


/**
 * Description of 3
 *
 * @author gunawan
 */
class menu {
    //put your code here
    private $menu;
    function __CONSTRUCT(){
        $menu = array(
            'top' => array(
                array(6, 'one menu'),
                array(1, 'multi menu')
            )
        );

        $menu['sub'] = array(
            '1' => array(
                array(2, 'one menu'),
                array(11, 'multi menu')
            )
        );
        $menu['sub'][11]=array(
                array(3, 'one menu'),
                array(4, 'multi menu')
            );
        $this->menu=$menu;
    }

    function get(){
        return $this->menu;
    }

    function run(){

        return $this->get_parent();
    }
    //=============FOKUS pada ini saja
    function get_parent(){//get_list
        /*
        $this->db->where('parent', "");
        $temp = $this->db->get('menu_navigation');
        $array = null;
        if($temp->num_rows() > 0){
            foreach ($temp->result_object() as $row) {
                if(($child = $this->get_child($row->id)) != null){
                    $row->child = $child;
                }
                $array[] = $row;
            }
        }
         *
         * pada dasarnya sama seperti di atas.. hanya agak penyesuaian
        */
        $data= $this->menu['top'];//or parent

        $raw=array();
        foreach($data as $row){
            $tmp = array('id'=>$row[0], 'text'=>$row[1]); //mending langsung dibuat gini walau dari query udah melakukannya
            $have_child=$this->have_child($row[0]);
            if($have_child){
                $tmp['child']=$this->get_child($row[0]);
            }
            $raw[]=$tmp;
        }
        return $raw;
    }

    function have_child($id){
        $child=$this->menu['sub'];
        return isset($child[$id])?TRUE:FALSE;
    }

    function get_child($id){
        $data_child= $this->menu['sub'];//or child
        $data=$data_child[$id]; //asumsikan kamu dapatkan dari query where parent=xxx
        $raw=array();
        foreach($data as $row){
            $tmp = array('id'=>$row[0], 'text'=>$row[1]); //mending langsung dibuat gini walau dari query udah melakukannya
            $have_child=$this->have_child($row[0]);
            if($have_child){
                $tmp['child']=$this->get_child($row[0]);
            }
            $raw[]=$tmp;
        }
        return $raw;
    }
}

$menu = new menu();

$ar = $menu->run();

echo '<pre>'.print_r($ar,1).  json_encode($ar);
/**** HASIL
Array
(
    [0] => Array
        (
            [id] => 6
            [text] => one menu
        )

    [1] => Array
        (
            [id] => 1
            [text] => multi menu
            [child] => Array
                (
                    [0] => Array
                        (
                            [id] => 2
                            [text] => one menu
                        )

                    [1] => Array
                        (
                            [id] => 11
                            [text] => multi menu
                            [child] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 3
                                            [text] => one menu
                                        )

                                    [1] => Array
                                        (
                                            [id] => 4
                                            [text] => multi menu
                                        )

                                )

                        )

                )

        )

)

jsonnya:
[

    {
        "id":6,
        "text":"one menu"
    },
    {
        "id":1,
        "text":"multi menu",
        "child":[
            {
                "id":2,
                "text":"one menu"
            },
            {
                "id":11,
                "text":"multi menu",
                "child":[
                    {
                        "id":3,
                        "text":"one menu"
                    },
                    {
                        "id":4,
                        "text":"multi menu"
                    }
                ]
            }
        ]
    }

]



****/
/*
    function get_list(){
        $this->db->where('parent', "");
        $temp = $this->db->get('menu_navigation');
        $array = null;
        if($temp->num_rows() > 0){
            foreach ($temp->result_object() as $row) {
                if(($child = $this->get_child($row->id)) != null){
                    $row->child = $child;
                }
                $array[] = $row;
            }
        }
        return $array;
    }

    function get_child($id){
        $this->db->where('parent', $id);
        $temp = $this->db->get('menu_navigation');
        $array = null;
        if($temp->num_rows() > 0){
            foreach ($temp->result_object() as $row) {
                $array[] = $row;
            }
        }
        return $array;
    }
    */

?>