In this data structure, each node stores a point in R k and the index of the dimension (axis) used to partition the data at that node. Points whose coordinate in the chosen dimension is less than that of the pivot go to the left subtree, while points with a larger coordinate go to the right subtree. The axis to split along usually cycles through 0, 1, . . . , k -1, ensuring a round-robin partitioning scheme. The result is a binary tree whose height is on average O(log N ) for balanced data. In the worst case, the tree can degrade to O(N ) height if many points cluster in unfavorable ways.