my %tree = (
  "Office of President" => {
    Recruiting  => undef,
    'Pipe line' => undef,
    Software    => {
      MIS                 => undef,
      'System Operations' => undef,
    },
  }
);

print dump_tree(\%tree);

sub dump_tree {
  my($tree, $indent) = ( $_[0], $_[1] || 0 );

  my $ret = '';
  for(sort keys %$tree) {
    $ret .= " " x $indent."$_\n";
    $ret .= dump_tree($tree->{$_}, $indent + 2)
      if ref $tree->{$_} and ref $tree->{$_} eq 'HASH';
  }

  return $ret;
}

__output__

Office of President
  Pipe line
  Recruiting
  Software
    MIS
    System Operations