Soap server that has the Tree object:

---

use SOAP::Lite +trace =>
    'all';
use SOAP::Transport::HTTP;

use Node;

# don't want to die on 'Broken pipe' or Ctrl-C
$SIG{PIPE} = $SIG{INT} = 'IGNORE';

$daemon = SOAP::Transport::HTTP::Daemon
    -> new (LocalPort => 8080)
    -> objects_by_reference('Node')
    -> dispatch_to('Node');

print "Contact to SOAP server at ", $daemon->url, "\n";
$daemon->handle;
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---

Soap client that builds the tree on the server:

---

use SOAP::Lite +autodispatch =>
    uri => 'urn:',
    proxy => 'http://localhost:8080/'
;

my $root = new Node(12);
print $root->toString(), "\n";

for (my $i = 0; $i < 3; $i++) {
    my $child = new Node($i+1);
    print $child->toString(), "\n";
    $root->addChild($child);
    print $root->toString(), "\n";
}

my $aChild = $root->child(1);
my $aParent = $aChild->parent();

print $aParent->toString(), "\n";
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---

and the Node class to build the tree from:

---

package Node;

use strict;

sub new {
    my ($pkg, $value) = @_;
    my $node = bless {
        value => $value,
        parent => undef,
        nrChildren => 0,
        children => []
        }, $pkg;
    return $node;
}

sub addChild {
    my ($node, $child) = @_;
    $node->{children}->[$node->{nrChildren}++] = $child;
    $child->{parent} = $node;
}

sub numberOfChildren {
    my ($node) = @_;
    return scalar(@{$node->{children}});
}

sub child {
    my ($node, $index) = @_;
    return $node->{children}->[$index];
}

sub parent {
    my ($node) = @_;
    return $node->{parent};
}

sub toString {
    my ($node) = @_;
    return "node[$node->{value}]: " . scalar(@{$node->{children}}) . "
+ children";
}

1;
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---

Note that the client and the server need not run on the same machine as in the example code (this was actually tested).