Techniques for tuning the key space of an instance of a tree data structure are provided. In one embodiment, a computer system can receive a request to create the instance, where the request includes an expected key space value indicating an expected range of key values to be addressed by the instance. The computer system can further calculate a number of bits to allocate to each key of each node of the instance based on the expected key space value. The computer system can then, at a time of instantiating each node of the instance, allocate the keys for the node in accordance with the calculated number of bits.