src/Baum/Node.php
public static function roots() {
    $instance = new static;

    return $instance->newQuery()
                    ->whereNull($instance->getParentColumnName())
                    ->orderBy($instance->getQualifiedOrderColumnName());
  }
public static function roots() {
    $instance = new static;

    return $instance->newQuery()
                    ->whereNull($instance->getParentColumnName())
                    ->orderBy($instance->getQualifiedOrderColumnName());
  }
Static query scope. Returns a query scope with all root nodes.

@return \Illuminate\Database\Query\Builder