#!/app/perl5.005/bin/perl
use strict;
use Data::Dumper;

sub add2hash {
  my($hash,$value,@tree)=@_;

  my $tree='$hash->{'.join('}{',@tree)."}=$value";
  eval $tree;
}

my(%tree);
add2hash(\%tree,1,('a'..'c'));
add2hash(\%tree,2,('a','b','d'));
print Dumper(\%tree);