<?php # -*- coding: utf-8 -*-
/**
 * Plugin Name: Make it work
 */
add_action( 'admin_print_footer_scripts', 't5_make_it_work' );
function t5_make_it_work(){	?>
<script>jQuery(function($) {
	var css = {
		'padding':    '0 20px',
		'cursor':     'pointer',
		'background': '#080',
		'color':      '#fff'
	};
	var miw = $('<li>Make it work!</li>').css(css).click(function(){alert('It works!');});
	$('#wp-admin-bar-top-secondary').append(miw);
});</script><?php
}

terms are returned like:

level1
    level2
        level3
        level3
level1
    level2
        level3

so I need:

[1] = (
    [2] = (
        3,4
    )
)
[5] = (
    [6] = (
        7,8
    )
)

level1 = array(1,5)
level2 = array(2,6)
level3 = array(3,4,7,8)

array (
0 =>
stdClass::__set_state(array(
 'term_id' => '31',
 'parent' => '26'
)),
1 =>
stdClass::__set_state(array(
 'term_id' => '3',
 'parent' => '0'
)),
2 =>
stdClass::__set_state(array(
 'term_id' => '32',
 'parent' => '26'
)),
3 =>
stdClass::__set_state(array(
 'term_id' => '33',
 'parent' => '26'
)),
4 =>
stdClass::__set_state(array(
 'term_id' => '34',
 'parent' => '26'
)),
5 =>
stdClass::__set_state(array(
 'term_id' => '26',
 'parent' => '3'
)),

            $level = 0;
            $stack = $terms;
            $items = count( $stack );
            $count = -1;
            $end_game = array();
            while( $stack )
            {
                $count++;

                // Have we been through them all?
                if( $count == $items )
                {
                    $items = count( $stack );
                    $count = -1;
                    $level++;
                }

                $this_term = array_pop( $stack );

$output  = array();
$current = array( 0 );
$index   = 0;

while ( ! empty( $data ) ) {
	$parents        = $current;
	$current        = array();
	$output[$index] = array();

	foreach ( $data as $key => $term ) {
		if ( in_array( $term['parent'], $parents ) ) {
			$output[$index][] = $term['term_id'];
			$current[]        = $term['term_id'];
			unset( $data[$key] );
		}
	}

	$index ++;
}