use Data::Dumper;

my $tree_in = '(A,(B,C))';
#my $tree_in = "((A,(B,((C,(D,E)),(F,G)))),H)";

$tree_in =~ s/([^,()]+)/\{VALUE=>"$1"\}/g;
$tree_in =~ s/\(/\{LEFT=>/g;
$tree_in =~ s/,/,RIGHT=>/g;
$tree_in =~ s/\)/\}/g;

print $tree_in, "\n";
my $tref = eval $tree_in;
print Dumper $tref;
__END__
{LEFT=>{VALUE=>"A"},RIGHT=>{LEFT=>{VALUE=>"B"},RIGHT=>{VALUE=>"C"}}}
$VAR1 = { 
          'LEFT' => { 
                      'VALUE' => 'A'
                    },
          'RIGHT' => { 
                       'LEFT' => { 
                                   'VALUE' => 'B'
                                 },
                       'RIGHT' => { 
                                    'VALUE' => 'C'
                                  }
                     }
        };