use warnings;
use strict;

my @tab;

while(my $l = readline (*DATA) ) {
     @{$tab[$.-1]}= split '',$l ;
     foreach my $i (0..$#{$tab[$.-1]})  {
         unless ($. == 1) { ${$tab[$.-1]}[$i] =~ s/\|/${$tab[$.-2]}[$i
+]/g if defined ${$tab[$.-2]}[$i]  }
     }
}

foreach my $row (@tab) {
        print @{$row};
}
__DATA__
A
|
|--B
|  |
|  |--C
|     |
|     |---PQR
|     |---XYZ
|--D
|  |
|  |---LMN
|---XYZ
X
|---000
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