Jarves\Admin\ObjectCrud::getTreeFields PHP Method

    public function getTreeFields($fields = null)
    {
        //use default fields from object definition
        $definition = $this->objectDefinition;
        $fields2 = array();
        if ($fields && $this->getAllowCustomFieldSelection()) {
            if (is_array($fields)) {
                $fields2 = $fields;
            } else {
                $fields2 = explode(',', trim(preg_replace('/[^a-zA-Z0-9_,]/', '', $fields)));
            }
        }
        if ($definition && !$fields2) {
            if ($treeFields = $definition->getTreeFields()) {
                $fields2 = explode(',', trim(preg_replace('/[^a-zA-Z0-9_,]/', '', $treeFields)));
            } else {
                $fields2 = $definition->getDefaultSelection() ? explode(',', trim(preg_replace('/[^a-zA-Z0-9_,]/', '', $definition->getDefaultSelection()))) : array();
            }
            $fields2[] = $definition->getSingleItemLabelField();
            if ($definition->getTreeIcon()) {
                $fields2[] = $definition->getTreeIcon();
            }
        }
        return $fields2;
    }