Build a tree from collection of elements

buildVisialTree.php

<?php
$events = [
    ["id" => 14, "name" => 'root event', "parent_id" => 0],
    ["id" => 15, "name" => 'an event', "parent_id" => 14],
    ["id" => 33, "name" => 'a sub event', "parent_id" => 15],
    ["id" => 52, "name" => 'a sub event (2)', "parent_id" => 33],
    ["id" => 68, "name" => 'another root event', "parent_id" => 0],
    ["id" => 83, "name" => 'yet another root event', "parent_id" => 0],
    ["id" => 84, "name" => 'another sub event', "parent_id" => 83],
    ["id" => 87, "name" => 'another sub event (x)', "parent_id" => 83],
];

function buildDataTree(array &$elements, $parentId = 0): array
{
    $branch = [];

    foreach ($elements as $element) {
        if ($element['parent_id'] === $parentId) {
            $children = buildDataTree($elements, $element['id']);
            if ($children) {
                $element['children'] = $children;
            }
            $branch[$element['id']] = $element;
            unset($elements[$element['id']]);
        }
    }
    return $branch;
}

$tree = buildDataTree($events);

function buildVisualTree($tree, $level = 0)
{
    $options = '';
    foreach ($tree as $event) {
        $pad = '·';
        $line = "{$event['id']}: {$event['name']} ({$event['parent_id']})";
        $options.= str_repeat($pad, 2 * $level). $line . PHP_EOL;

        if (isset($event['children'])) {
            $options .= buildVisualTree($event['children'], ++$level);
            $level = 0;
        }

    }
    return $options;
}

echo buildVisualTree($tree);

// 14: root event (0)
// ··15: an event (14)
// ····33: a sub event (15)
// ······52: a sub event (2) (33)
// 68: another root event (0)
// 83: yet another root event (0)
// ··84: another sub event (83)
// ··87: another sub event (x) (83)

Given a collection of elements with an id and a parent_id, sort them as a tree (array) and then build a string out of them to print out.
The padding char can be replaced to whatever you may need.

# (id): name (parent_id)

14: root event (0)
··15: an event (14)
····33: a sub event (15)
······52: a sub event (2) (33)
68: another root event (0)
83: yet another root event (0)
··84: another sub event (83)
··87: another sub event (x) (83)