  We explore the timing and spectral properties of GRS 1915+105 based on X-ray
observations of NICER and Insight-HXMT during the long outburst from 2017 to
2021. We find a new class of variability in the rising stage of the outburst
that differs from the formerly reported patterns of light curves. This new
variability pattern, which we name class $\psi$, is characterized by several
periodic mini pulses superposed on another longer periodic pulse. The periods
are around $\sim$130 seconds and $\sim$10 seconds for the main pulses and mini
pulses respectively based on the analysis of power spectrum density (PSD) and
step-wise filter correlation (SFC), where the SFC method has an advantage in
finding the superimposed periodic components. The mini pulses become weak or
disappear when the luminosity increases and the light curves change into the
classical class $\kappa$. The class $\psi$ shows a softer spectrum with lower
count rates compared to the class $\kappa$ during the main pulse. The new class
$\psi$ shows peculiar timing and spectral properties compared to those of
classic class $\kappa$, which can help us to explore the class transition
mechanism in GRS 1915+105.
