Yup, roughly four lines shorter reimplementing (virtually) the same approach (not counting shebangs, use strict-y pragmata, or blank lines). Not to mention things like I don't yet grok Clojure / FP well enough that I can do in it what my $t = \%tree; while( @parts ) { my $head = shift @parts; $t = ($t->{$head} ||= {}); } lets me do trivially in Perl, or a better way than (apply str (repeat indent " ") to do " " x $indent.

The Perl version is certainly much "slimmer" than my Clojure (and less . . . "chatty"? "visually cluttered"?) at roughly half the number of characters:

$ wc *
      44     152    1258 tree.clj
      42     112     741 tree.plx
      86     264    1999 total
[download]

Also the OP had said they were trying to build a tree and traverse it; your above approach doesn't give a data structure that can be manipulated afterwards or walked multiple times (not that it's not shorter and yours preserves the original ordering (unlike mine), just that's what I read the OP as looking for).