  YbPtBi is one of the heavy-fermion systems with largest Sommerfeld
coefficient $\gamma$ and is thus classified as a `super'-heavy fermion
material. In this work, we resolve the long-debated question about the
hierarchy of relevant energy scales, such as crystal-electric field (CEF)
levels, Kondo and magnetic ordering temperature, in YbPtBi. Through
measurements of the a.c. elastocaloric effect and generic symmetry arguments,
we identify an \textit{elastic level splitting} that is uniquely associated
with the symmetry-allowed splitting of a quartet CEF level. This quartet, which
we identify to be the first excited state at $\Delta/k_\text B\approx1.6\,\rm
K$ above the doublet ground state at ambient pressure, is well below the Kondo
temperature $T_\text K\approx10\,\rm K$. Thus, our analysis provides strong
support for models that predict that the heavy electron mass is a result of an
enhanced degeneracy of the CEF ground state, i.e., a quasi-sextet in YbPtBi. At
the same time, our study shows the potential of the a.c. elastocaloric effect
to control and quantify strain-induced changes of the CEF schemes, opening a
different route to disentangle the CEF energy scales from other relevant energy
scales in correlated quantum materials.
