protected function _getSubTree(Model $model, $id = null) {
		$result = [];
		$parentField = $this->_getBehaviorConfig($model, 'parent');
		$leftField = $this->_getBehaviorConfig($model, 'left');
		if (($parentField === null) || ($leftField === null)) {
			return $result;
		}

		$conditions = [
			$model->alias . '.' . $parentField => null
		];
		if (!empty($id)) {
			$conditions[$model->alias . '.' . $parentField] = (int)$id;
		}
		if ($model->Behaviors->Tree->settings[$model->alias]['scope'] !== '1 = 1') {
			$conditions[] = $model->Behaviors->Tree->settings[$model->alias]['scope'];
		}

		$fields = [
			$model->alias . '.' . $model->primaryKey,
		];
		$order = [
			$model->alias . '.' . $leftField => 'asc'
		];
		$model->recursive = -1;
		$data = $model->find('list', compact('conditions', 'fields', 'order'));
		if (!empty($data)) {
			$result = array_keys($data);
		}

		return $result;
	}