def METHOD_NAME(operation_tree: OP_TREE) -> npt.NDArray[np.complex64]:
    """Returns the density matrix of the Choi state associated to the
    input operation tree (e.g. a single operation or a sequence of operations).
    The density matrix completely characterizes the quantum channel induced by
    the input operation tree (including the effect of noise if present).
    Args:
        operation_tree: Nested list of operations.
    Returns:
        The density matrix of the Choi state associated to the input circuit.
    """
    circuit = Circuit(operation_tree)
    return _circuit_to_choi(circuit)