use strict;
use warnings;
use Data::Dumper;

sub add_to_hash {
	my $hash=my $root=(ref $_[0] ? shift : {});
        	
	my $last=pop;
        
	for my $key (@_) {
		$hash=($hash->{$key}||={});
		die "Eeek, not a ref!" unless ref $hash;
	}
	$hash->{$last}=1;
	return $root;
}

my %hash;

add_to_hash(\%hash,qw(a b c d));
add_to_hash(\%hash,qw(a c d e));

print Dumper(\%hash);