Resolve nodes to tree.

nodes_to_tree.php

<?php
/**
 * Created by PhpStorm.
 * User: dailybird
 * Date: 17/6/1
 * Time: 下午11:57
 */


$nodes = [
    [
        'id' => 5,
        'parent_id' => 2
    ],
    [
        'id' => 2,
        'parent_id' => 1
    ],
    [
        'id' => 3,
        'parent_id' => 1
    ],
    [
        'id' => 1,
        'parent_id' => -1
    ],
    [
        'id' => 6,
        'parent_id' => 4
    ],
    [
        'id' => 8,
        'parent_id' => 7
    ],
    [
        'id' => 9,
        'parent_id' => 7
    ],
    [
        'id' => 7,
        'parent_id' => 4
    ],
    [
        'id' => 10,
        'parent_id' => 4
    ],
    [
        'id' => 4,
        'parent_id' => -1
    ],
];


function resolveNodesToTree(&$tree, &$nodes, $parentNode)
{
    foreach ($nodes as $index => $node) {
        if($node['parent_id'] === $parentNode){
            $foo = resolveNodesToTree($tree[$node['id']], $nodes, $node['id']);
            if(!is_null($foo)){
                $node['children'] = $foo;
                $tree[] = $node;
                unset($nodes[$index]);
            }else{
                unset($tree[$node['id']]);
            }
        }
    }
    return $tree;
}

const ROOT_NODE = -1;
$tree = [];
resolveNodesToTree($tree, $nodes, ROOT_NODE);

print_r(json_encode($tree));