#!/usr/bin/perl -w
my $tree={};

# warning: recursive subroutine
sub insert {
  my ($tree,$val,@keys)=@_;
  my $key=shift @keys;
  unless (defined($tree->{$key})) {
    $tree->{$key}={};
  }
  if (scalar @keys) {
    insert($tree->{$key},$val,@keys);
  } else {
    $tree->{$key}=$val;
  }
}
  
insert($tree,'1',qw(a b c d)); # test 1
insert($tree,'2',qw(a b d e)); # test 2
insert($tree,$val,split(':',$key); # the call you were looking for.