I don't know what that means. I'm assuming a random element of the tree is picked, that parent nodes are in a smaller or equal cache level than children, that all but one cache levels are used completely, that each cache level has O(sqrt n) access time, and that there is an upper bound on the ratio between successive cache sizes.

Or less generally: it takes sqrt(j) nanoseconds to dereference the pointer with value j, and parent nodes are at smaller addresses than their children.