sub search {
  my ($tree, $val) = @_;
  return $tree if $val < $tree->{weight};
  $val -= $tree->{weight};
  return search($tree->{left}, $val) if $val < $tree->{left}->{total_weght};
  $val -= $tree->{left}->{total_weight};
  return search($tree->{right}, $val);
}