use Data::Dumper;

my @stack;
my %hash;
push @stack, \%hash;
while(<DATA>){
    chomp;
    s/^(\t*)//;
    splice @stack, length($1)+1;
    push @stack, $stack[$#stack]->{$_} = {};
}

print Dumper(\%hash);


__DATA__
foo
        sub1
        sub2
                sub21
                sub22
bar
        camel

##</code><code>##

$VAR1 = {
          'foo' => {
                     'sub1' => {},
                     'sub2' => {
                                 'sub21' => {},
                                 'sub22' => {}
                               }
                   },
          'bar' => {
                     'camel' => {}
                   }
        };