code: public function getDescendants($columns = array('*')) {
      if ( is_array($columns) )
        return $this->descendants()->get($columns);
  
      $arguments = func_get_args();
  
      $limit    = intval(array_shift($arguments));
      $columns  = array_shift($arguments) ?: array('*');
  
      return $this->descendants()->limitDepth($limit)->get($columns);
    }
docs: Retrieve all of its children & nested children.
  
  @param  array  $columns
  @return \Illuminate\Database\Eloquent\Collection