CHILDREN_PER_NODE
t->counts[i] = dm_div_up(t->counts[i + 1], CHILDREN_PER_NODE);
t->depth = 1 + int_log(leaf_nodes, CHILDREN_PER_NODE);
return (n * CHILDREN_PER_NODE) + k;
n = get_child(n, CHILDREN_PER_NODE - 1);