OctoberCMS model Convert SimpleTree to NestedTree https://octobercms.inetis.ch/convert-your-model-data-simpletree-nestedtree

convertToNestedTree.php

<?php

/**
 * This script convert a model using 
 * \October\Rain\Database\Traits\SimpleTree to 
 * \October\Rain\Database\Traits\NestedTree
 * 
 * Before run create required fields in your DB for NestedTree 
 * ( https://octobercms.com/docs/database/traits#nested-tree )
 */

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

        // Add `->sortBy('sort_order')` if you have a custom sort column
        $children = $item->getChildren();

        buildTree($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())
    // ->orderBy('sort_order') if you have a custom sort column
    ->get();

buildNestedTree($roots, $level, $nest);