This is how I deal with the leaf/node problem. Each level is an array ref, where the first element of the array is the hash ref for the next level, while the second element (if any) is the leaf value (if any).

use Data::Dumper;

my %shash;

foreach my $line (<DATA>) {
   # Get rid of end of line.
   chomp($line);

   # Build hash from line.
   my (@items) = split /--/, $line;
   @items or next;

   my $p = \%shash;       # Start at root node
   while (@items > 1) {
     my $i = shift @items;
     $p->{$i}[0] ||= {};  # Create new node if necessary
     $p = $p->{$i}[0];    # Point at new node
   }
   my $i = shift @items;  # Get last item
   $p->{$i}[1] = $i;      # Make it a leaf of the last node
}

print(Dumper(\%shash));

__DATA__
Item1--Item2--Item3
ItemX--Item2--ItemA
Item1--ItemV--Item3--Item4
Item1--Item2--Item3--Dup!
ItemX
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