quadtree.cover(x, y) Expands the quadtree to cover the specified point ⟨x,y⟩, and returns the

quadtree.data() Returns an array of all data in the quadtree.

quadtree.remove(datum) Removes the specified datum to the quadtree, deriving its coordinates ⟨x,y⟩

quadtree.size() Returns the total number of data in the quadtree.

quadtree.add(datum) Adds the specified datum to the quadtree, deriving its coordinates ⟨x,y⟩

quadtree.root() Returns the root node of the quadtree.