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