<?php
$array = [
	'hello' => 'world',
	'doing' => [
		 'hello' => 'universe',
		 'going' => [
		 	'hello' => 'existence'
		 ],
		 'moving' => [
		 	 'answer' => 42,
		 ]
    ]
];
function levelUp(&$array, $level = 1) {
	$array['id'] = $level;
	foreach($array as $key => &$value) {
		if(is_array($value)) {
			levelUp($value, $level + 1);
		}
	}
}
levelUp($array);

var_dump($array);
// your code goes here