use strict;
use warnings;
use Data::Dump 'pp';

my %hash;

$hash{tree}->{apple} = 6;
pp \%hash;

$hash{tree} = {apple => 6};
pp \%hash;

__END__
{ tree => { apple => 6 } }
{ tree => { apple => 6 } }

##</code><code>##

use strict;
use warnings;
use Data::Dump 'pp';

my %hash;

$hash{tree} = [4];
push @{$hash{tree}}, {apple => [6]};

pp \%hash;

my $apple_tree = $hash{tree}->[1]->{apple};
push @$apple_tree, {red => 9, fuju => 4};

pp \%hash;

__END__
{ tree => [4, { apple => [6] }] }
{ tree => [4, { apple => [6, { fuju => 4, red => 9 }] }] }

##</code><code>##

for my $key (keys %hash) {
    my ($root_value, $subtree) = @{$hash{$key}};
    print "$key  $root_value\n";

    for my $subtree_key (keys %$subtree) {
        my ($subtree_root_value, $subtree_subtree) = @{$subtree->{$subtree_key}};
        print "$key  $subtree_key  $subtree_root_value\n";

        for my $bottom_level_key (keys %$subtree_subtree) {
            print "$key  $subtree_key  $bottom_level_key  ", $subtree_subtree->{$bottom_level_key}, "\n";
        }
    }
}

__END__
tree  4
tree  apple  6
tree  apple  fuju  4
tree  apple  red  9