The following is a fairly simple-minded technique for building the tree and performing preorder and postorder traversals.

#! /usr/bin/perl -w

use strict;
use Data::Dumper;

$Data::Dumper::Indent = 1;

my %tree;

while( <DATA> ) {
    chomp;
    my $t = \%tree;
    my @char = split //;
    for( @char ) {
        $t->{$_} = {} unless exists $t->{$_};
        $t = \%{$t->{$_}};
    }
}

sub pre_traverse {
    my $t = shift;
    for my $k( sort keys %$t ) {
        print "$k ";
        pre_traverse( $t->{$k} );
    }
}

sub post_traverse {
    my $t = shift;
    for my $k( sort keys %$t ) {
        post_traverse( $t->{$k} );
        print "$k ";
    }
}


print "PRE: ";
pre_traverse(\%tree),

print "\nPOST: ";
post_traverse(\%tree),

print "\n", Dumper(\%tree), "\n";

__DATA__
aB1
aB2
aB4j
aB8
aC3
aC50
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This produces the following:

PRE: a B 1 2 4 j 8 C 3 5 0
POST: 1 2 j 4 8 B 3 0 5 C a
$VAR1 = {
  'a' => {
    'C' => {
      '3' => {},
      '5' => {
        '0' => {}
      }
    },
    'B' => {
      '8' => {},
      '4' => {
        'j' => {}
      },
      '1' => {},
      '2' => {}
    }
  }
};
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