my $count = scalar @$expanded;
$expanded = [ 
  map { 
    my $row = $_;
    map { 
      my $newrow = {%$row};
      @$newrow{keys %$_} = values %$_ unless $newrow->{$parent_key};
      $newrow }  @$expansion ;
  } @$expanded ];

push @$expanded,  @$expansion if $count == scalar @$expanded;