void customMethod();
    }

    /**
     * Extended SmbTree interface for testing nested unwrapping.
     */
    interface ExtendedSmbTree extends SmbTree {
        void extendedMethod();
    }

    /**
     * Incompatible tree type for testing type incompatibility.
     */
    interface IncompatibleTree extends SmbTree {
        void incompatibleMethod();
    }