Hi Boldra, the following can obviously be golfed but left this way for clarity.

use strict; 
my %hash;
my @array=qw(one 1 two 2 two 20);
for (my $i=0;$i<@array;$i+=2){
   push @{$hash{$array[$i]}}, $array[$i+1];
}
for my $key( keys %hash){
   print "$key => @{$hash{$key}}\n";
}
[download]

UPDATE: Apologies to ELISHEVA whose answer above is almost identical with the added benefit of golfing too, I took far to long to reply and so hadn't seen that response