sub find_key_dupes {
  my $binary_tree=shift;
  my $key=shift;
  my $sub;
  my @dupes;
  $sub=sub {
              my $node=shift;
              return unless $node;
              if ($node->{key} lt $key) {
                  $sub->($node->{right});
              } else {
                  push @dupes,$node if $node->{key} eq $key;
                  $sub->($node->{left});
              }
           };
  $sub->($binary_tree);
  return \@dupes;
}