I can't comment on your data structures, because I can't see them. But basic program flow from your example confirms that it will never work properly. You call displaynames with one variable:

$self->displaynames($self->{root});
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But displaynames needs two variables to work:

sub displaynames
{       my $self = shift;
        $head = shift;
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If $head isn't defined, the rest of the routine does not run, and no 'child' nodes are called. Either call displaynames with two arguments, or remove those if statements.

Update: And either you are running without strict or you have defined '$head' as a global, both are bad.

____________________
Jeremy
I didn't believe in evil until I dated it.