You haven't given us any idea of what you actually need to do with this data, and it's actually not clear to me that Tree::Parser is the right tool for this data (or for whatever you actually need to do with it). In fact, having scanned the Tree::Parser man page, my first impression is that it's not a good match for your data -- if I'm wrong about that, I'll be interested in finding out why.

If you are starting with a flat hash (or hash of arrays) and you want to build a tree-style hash, the basic plan would be to turn it into a recursive HoH structure, such that every "leaf" node in the tree is just an empty hash ref. Something like:

use strict;
use warnings;
use Data::Dumper 'Dumper';

my %tree;
while (<DATA>) {
    chomp;
    next unless ( /^\s*(\d+)\s*=>\s*(.*)/ );
    my ( $key, $val ) = ( $1, $2 );
    if ( $val eq '' ) {  # leaf node
        $tree{$key} = {} unless exists( $tree{$key} );  # assign an em
+pty hash ref
    }
    else {
        for my $node ( split /, +/, $val ) {
        if ( ! exists( $tree{$node} )) {
        $tree{$node} = {};
        }
        $tree{$key}{$node} = \$tree{$node};
        push @{$tree{$node}{parent}}, $key; # keep track of node paren
+ts
        }
    }
}

# all done:
for ( sort keys %tree ) {
    print "======\n$_:\n", Dumper( $tree{$_} ) unless exists( $tree{$_
+}{parent} );
}

# append your data below...
__DATA__
[download]

That includes a "parent" element for every node that has one or more parents, to make it easier to keep track of relations. I'm not sure if that's what you're looking for...