my %hash;

for (@bigArray) {
  @tmp = split(\\+/);   # split by '+'
  $node = 'value';
  $node = {$_=>$node} foreach reverse @keys;
  ....
}

##</code><code>##


my @bigArray = qw(brown red+green blue+yellow black red+white purple+orange+gray);

##</code><code>##

%hash = (
         brown => 1,
         red => (
                 green => 1,
                 white => 1,
                ),
         blue => (
                  yellow => 1,
                 ),
         black => 1,
         purple => (
                    orange => (
                               gray => 1,
                              ),
                   ),
         );