Construct a binary tree
• At each step, choose one of the coordinate as a basis of dividing the
rest of the points
• For example, at the root, choose x as the basis
– Like binary search trees, all items to the left of root will have
the x-coordinate less than that of the root
– All items to the right of the root will have the x-coordinate
greater than (or equal to) that of the root
• Choose y as the basis for discrimination for the root’s children
• And choose x again for the root’s grandchildren
Note: Equality (corresponding to right child) is significant