use strict;
my @paths = (
          'C:\\foo\\bar\\baz',
          'C:\\foo\\bar',
          'C:\\car',
          'C:\\c'
        );

my $last = "";
my @nested;
for (sort @paths) {
    if (not @nested) {
        push @nested, $_;
    } elsif (/^\Q$nested[-1]\E\\/i) {
        $nested[-1] = $_;
    } else {
        push @nested, $_;
    };
};
print "$_\n" for @nested;