how to use this recursive code in codeigniter - codeigniter

Question

db_connection.php
<?php
define('_HOST_NAME', 'localhost');
define('_DATABASE_USER_NAME', 'root');
define('_DATABASE_PASSWORD', '');
define('_DATABASE_NAME', 'test_database');
$dbConnection = new mysqli(_HOST_NAME, _DATABASE_USER_NAME, _DATABASE_PASSWORD, _DATABASE_NAME);
if ($dbConnection->connect_error) {
trigger_error('Connection Failed: ' . $dbConnection->connect_error, E_USER_ERROR);
}
$_GLOBAL['dbConnection'] = $dbConnection;
?>
function.php
<?php
function categoryParentChildTree($parent = 0, $spacing = '', $category_tree_array = '') {
global $dbConnection;
$parent = $dbConnection->real_escape_string($parent);
if (!is_array($category_tree_array))
$category_tree_array = array();
$sqlCategory = "SELECT id,name,parent_id FROM tbl_categories WHERE parent_id = $parent ORDER BY id ASC";
$resCategory=$dbConnection->query($sqlCategory);
if ($resCategory->num_rows > 0) {
while($rowCategories = $resCategory->fetch_assoc()) {
$category_tree_array[] = array("id" => $rowCategories['id'], "name" => $spacing . $rowCategories['name']);
$category_tree_array = categoryParentChildTree($rowCategories['id'], ' '.$spacing . '- ', $category_tree_array);
}
}
return $category_tree_array;
}
?>
index.php
<?php
require_once 'db_connection.php';
require_once 'functions.php';
$categoryList = categoryParentChildTree();
foreach($categoryList as $key => $value){
echo $value['name'].'<br>';
}
?>
can anyone help me to translating this so i can use on codeigniter? recursive function
sorry im new on codeigniter
please help