my @textsplit= split /\./, $text;
my $p= pop @textsplit;
foreach (reverse @textsplit) {
  my $new->{$_}= $p;
  $p= $new;
}
[download]

But this naturally won't work if you want to convert many text lines with common parts (i.e. "a.b.c.d" and "a.b.n.m") and want to get one single data structure out of it

UPDATE: davido found a bug in my code. Corrected with addition of $new.