my %global_data;
fill_recursively(\%global_data, 10);
sub fill_recursively {
  my $data_href = shift; # hashref to modify
  my $count = shift; # what level are we
  push @{$data_href->{"key $_"}}, "level $count" for 1..$count;
  fill_recursively($data_href, $count - 1) if $count > 1;
}
use Data::Dumper;
print Dumper(\%global_data);