I am new to perl and I have the following script. 
$tree = <>; chop($tree); 
while ($tree=~s/\(?([A-Z])([A-Z])\)?/\1/) {
    print $tree;
    print "\n";
}

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When I run this program with input (A((BC)D)(EF)), i get the following output, which I don't understand. Can some explain this regular expression 
(A(BD)(EF))
(AB(EF))
A(EF))
AE)
A

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In reply to Interpretation of my output by musa

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