FIXED VERSION OF OctoberCMS model Convert SimpleTree to NestedTree https://octobercms.inetis.ch/convert-your-model-data-simpletree-nestedtree taken from https://octobercms.inetis.ch/convert-your-model-data-simpletree-nestedtree

convertToNestedTree.php

/*
 * This script migrate model data from SimpleTree to NestedTree
 *
 * @see \October\Rain\Database\Traits\SimpleTree
 * @see \October\Rain\Database\Traits\NestedTree
 *
 * Before executing this ensure that your model implement SimpleTree 
 * and switch to NestedTree only when the process is complete
 */

function buildNestedTree($items, $level, &$nest)
{
    $items->each(function ($item) use (&$nest, $level) {
        $item->nest_left = $nest++;
        $item->nest_depth = $level;

        $children = $item->getChildren();
        buildNestedTree($children, $level + 1, $nest);

        $item->nest_right = $nest++;
        $item->save();
    });
}

// Your model that implement \October\Rain\Database\Traits\SimpleTree
$model = new \VendorCode\PluginName\Models\YourModel();

$level = 0;
$nest = 1;

$roots = $model->whereNull($model->getParentColumnName())->get();

// Build the Tree from parents and goes down gradually
buildNestedTree($roots, $level, $nest);