For the sake of argument, let's say that world zero (W0 for short) is at some arbitrary level. Worlds being simulated below that level would be -W1, -W2, etc. Worlds above would be W1, W2, etc. If everything is deterministic then worlds at all levels take the same path and arrive at the same outcome. But if W0 has control over the -W1 timeline, then W0 can view it's own future by moving the -W1 timeline forward. W0 now knows it's own future (lottery numbers for arguments sake). W0 can now use that knowledge to change it's future. The W0 future is now different from the W1 future which contradicts the ability for all worlds to be deterministic.