  Electrons residing in flat-band system can play a vital role in triggering
spectacular phenomenology due to relatively large interactions and spontaneous
breaking of different degeneracies. In this work we demonstrate chirally
twisted triple bilayer graphene, a new moir\'e structure formed by three pieces
of helically stacked Bernal bilayer graphene, as a highly tunable flat-band
system. In addition to the correlated insulators showing at integer moir\'e
fillings, commonly attributed to interaction induced symmetry broken isospin
flavors in graphene, we observe abundant insulating states at half-integer
moir\'e fillings, suggesting a longer-range interaction and the formation of
charge density wave insulators which spontaneously break the moir\'e
translation symmetry. With weak out-of-plane magnetic field applied, as
observed half-integer filling states are enhanced and more quarter-integer
filling states appear, pointing towards further quadrupling moir\'e unit cells.
The insulating states at fractional fillings combined with Hartree-Fock
calculations demonstrate the observation of a new type of correlated charge
density wave insulators in graphene and points to a new accessible twist manner
engineering correlated moir\'e electronics.
