To give you a better sense for the geometric intuition behind this kd-tree, let's trace through what
happens when we try looking up whether a given point is in the kd-tree. In particular, let's see
what happens as we try to look up the node in the bottom-right corner of the kd-tree. We begin at
the root of the kd-tree and consider whether our node's x coordinate is less than or greater than the
root node's x coordinate. This is equivalent to splitting the plane vertically at the root node, then
asking which half-space our node is in. Our node happens to be in the right half-space, and so we
can ignore all of the nodes in the left half-space and recursively explore the right. This is shown
graphically below, where the grayed-out region corresponds to parts of the plane we will never
look in