D. Hume used the term "bundle" in this sense, also referring to the personal identity, in his main work: "I may venture to affirm of the rest of mankind, that they are nothing but a bundle or collection of different perceptions, which succeed each other with inconceivable rapidity, and are in a perpetual flux and movement".
And from thence comes the label, added by future readers, of "panphenomenalism". The below is actually a kind of unfolding "block universe" constituted of phenomenal properties/events rather than those "rational objects" of abstract, scientific description (i.e., "physical").
Panphenomenalism: David Hume (1711-1776) formulated the theory of Panphenomenalism. He denied the existence of all ultimate reality (metaphysical reality), accepting as valid data only those things experienced as sense impressions; in other words, he asserted that existence is limited to phenomena, which are objects, not of reason, but of experience. By rejecting the idea of cause and soul as substances, he eliminated the entire problem of interaction. Hume concluded that events depend upon merely repetitious or sequential activities; that nothing in the universe is ever created, or caused to act, by anything else; and that reality consists only of a series of phenomena appearing in a temporal order. --Ideas of the Great Philosophers; pages 107-108; by William S. Sahakian (1966)
Russellian Monism is akin to the above, or was inspired by it like the 19th-century scientists referenced in the quotes further down.
Note that for Hume, "phenomenal properties" (impressions) are prior in rank to "mind" and their constitution as a human identity. Considered apart from that role in the consciousness of organisms, phenomenal properties would be ontological (and fundamental) rather than mental, psychological, subjective, etc. An adjective like "onto-phenomenological" would emphasize such or help make the distinction of existing prior to recruitment by a brain for its special purposes.
Thus, Hume's panphenomenalism is not actually panpsychism. Due to the etymological "psyche" word-unit in the latter suggesting cognitive abilities being associated with matter in general. Philosophers need to cleanup their language to prevent misunderstandings like that.
Edward S. Reed: Matter for Huxley was just what it was for Mach or Hertz: a set of phenomenal observations made by scientists. It is thus remarkable but true that the most reviled "materialists" of the 1880s--Huxley, Tyndall, and Clifford--were all phenomenalists of sort or another and not materialists at all.
The positivist impulse gave new life to a variety of panphenomenalism, one whose adherents were surprisingly uncritical about the analysis of those allegedly basic mental phenomena, sensations. Thus, thinkers as different in outlook and interests as Huxley and Mach, Taine and Spencer, Wundt and Lewes all agreed that the basic "data" on which all science was to built were sensations. --From Soul to Mind: The Emergence of Psychology, from Erasmus Darwin to William James; p.161 by Edward S. Reed (1997)]
Edward S. Reed: [Thomas H.] Huxley, like all the other scientists in the group -- and like almost all scientists in Europe or America at the that time -- was not a materialist, despite his belief in the progress of mechanistic physiology. He argued in two directions: one from the external phenomena of science (say, the data of physiology) and the other from introspective phenomena (for example, our belief in free will). He was inclined to believe that most (or all) introspectively revealed phenomena would prove to be caused by externally revealed ones. But in any event he was a phenomenalist, arguing that what is real is phenomena. If the soul (or the unconscious) is not real, it is because it is not part of the phenomenal world.
This panphenomenalism was widely labeled positivism when it was propounded by scientists. In the loosely defined meandering of the term, positivism dominated the European intellectual scene from approximately 1870 to 1890. Yet that type of positivism is inherently unstable when applied to psychology. The externalist (physiological) analysis of behavior and mind attributes all psychological states to antecedent causes. Introspective analysis reveals both intuitions of freedom and the appearance of autonomous psychological states. The two seem irreconcilable. --same source as last, pages 121 to 122
Those phenomenalists, or their critics, or both, departed from Hume's original conception that phenomenal properties were prior in rank to mind -- similar to how the latter is considered today to emerge from non-mental matter. We make the error of classifying "qualia" (or their primitive precursors) as mental rather than ontological. Such manifestations would be the way that matter exists independent of our artificial mathematical or technical representations ("objects of reason"). Phenomenal properties should only acquire mental classification when they're recruited by the brain to construct our subjective mental experiences.
The other alternative, of phenomenal properties being magically conjured or summoned (brute emergence) by neural processes performing the correct "dance"... That is dualism, or obscured dualism. The latter should not be considered compatible with physicalism. That's the real point here -- that an explanation outputted by a particular metaphysics or methodological approach should at least be consistent with its own dogma, rather than ludicrously conflict with it.
Physicalism via its very meaning is supposed to keep the mystical, supernatural, whatever, out -- not indulge in it. Matter having an intrinsic way that it exists beyond artificial, abstract human symbols is simply commonsense, if _X_ truly believes in an objective or people-independent world.