  (abridged) A scenario for the formation of multiple co-eval populations
separated in age by about 1 Myr in very young clusters (VYCs, ages less than 10
Myr) and with masses in the range 600-20000 Msun is outlined. It rests upon a
converging inflow of molecular gas building up a first population of pre-main
sequence stars. The associated just-formed O stars ionise the inflow and
suppress star formation in the embedded cluster. However, they typically eject
each other out of the embedded cluster within 10^6 yr, that is before the
molecular cloud filament can be ionised entirely. The inflow of molecular gas
can then resume forming a second population. This sequence of events can be
repeated multiply. This model is applied to the Orion Nebula Cluster (ONC), in
which three well-separated pre-main sequences in the color-magnitude diagram of
the cluster have recently been discovered. The mass-inflow history is
constrained using this model and the number of OB stars ejected from each
population are estimated for verification using Gaia data. As a consequence of
the proposed model, the three runaway O star systems, AE Aur, mu Col and iota
Ori, are considered as significant observational evidence for stellar-dynamical
ejections of massive stars from the oldest population in the ONC.
