insert method
Insert a single (rowid, bbox) pair. Splits propagate up if needed.
Implementation
void insert(int rowid, BBox bbox) {
assert(bbox.dims == dims);
final sibling = _insert(_root, _Entry.leaf(rowid, bbox));
if (sibling != null) {
_root = _Node(false, [
_Entry.inner(_encloseNode(_root), _root),
_Entry.inner(_encloseNode(sibling), sibling),
]);
}
}