load method
Implementation
RBushDirect<T> load(Iterable<RBushElement<T>> items) {
if (items.any((item) => _boxes.containsKey(item))) {
throw StateError(
'Cannot have duplicates in the tree, use RBush class for that.');
}
_tree.load(items);
_boxes.addAll({for (final i in items) i.data: i});
return this;
}