use strict;
use warnings;

{
package bin_tree;
use strict;
use warnings;

sub new{
    my $class=shift;
    my $self={value=>shift, a=>undef, b=>undef};
    $self->{value}||=0;
    bless $self, $class; 
    return $self; 
}
sub a{
  my ($self, $setval) = @_;
  $setval or return $self->{a};
  return $self->{a} = $setval;
}
sub b{
  my ($self, $setval) = @_;
  $setval or return $self->{b};
  return $self->{b} = $setval;
}
sub populate{
    my($self, $depth, $value)=@_;
    return if(! $depth);
    $value ||= $self->{value};
    $self->a ( populate( bin_tree->new($value) , $depth -1 ) );
    $self->b ( populate( bin_tree->new($value) , $depth -1 ) );
    return $self;
}
sub depth{
	my ($self, $level)=@_;
    $level ||= 1;
	if (defined $self->a()){
	    return $self->a()->depth($level + 1);
	}
	return $level;
}
1;
} #end bin_tree

package main;

my $bintree = bin_tree->new('Initial') -> populate(3);
use Data::Dumper;
print "BEFORE: " ,Dumper ($bintree),"Depth:",$bintree->depth() ,"\n"; 

$bintree->a()->a()->populate(2,'Firstlevel')  -> b( bin_tree->new('secondlevel'));
print "After: ", Dumper ($bintree),"Depth:",$bintree->depth(), "\n";