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

my %hash;

foreach my $line (<DATA>)  #simulated simple CSV file
{
   my @cols = (split /,|\n/,$line);
   my $href = \%hash;
   
   while (my $col = shift @cols)
   {
       
       $href->{$col} = {} unless (exists ($href->{$col}) and 
                                  keys %{$href->{$col}} );
       
       $href = $href->{$col};    
   } 
}

print Dumper \%hash;

=OUTPUT:
$VAR1 = {
          'x' => {
                   '5' => {
                            '6' => {}
                          }
                 },
          'a' => {
                   'x' => {
                            'e' => {},
                            'm' => {},
                            'c' => {}
                          },
                   'b' => {
                            'c' => {}
                          },
                   'y' => {
                            'h' => {}
                          }
                 }
        };
=cut


__DATA__
a,x,c
a,x,e
a,y,h
a,x,m
a,b,c
x,5,6