$_ = q!0a { 1a { 1.1a } 1b { 1.2a    } 1c { 1.3a 1.3b }  } 0b { 2a { 2.1a}  } 0c!;
        
while(m!{[^{]+(({.*?})*)[^{]+}!g){
        $inside = $1; 
        print $&,"\n";
        while($inside =~ m!{[^{]+(({.*?})*)[^{]+}!g){
                print "\t",$&,"\n";
        }
}

##</code><code>##

$_ = q!0a { 1a { 1.1a } 1b { 1.2a    } 1c { 1.3a { 1.3.1a } 1.3b }  } 0b { 2a { 2.1a}  } 0c!;