  Long gamma-ray bursts have been widely associated with collapsing massive
stars in the framework of collapsar model. High-energy neutrinos and photons
can be produced in the internal shocks of middle relativistic jets from
core-collapse supernova. Although photons can hardly escape, high-energy
neutrinos could be the only signature when the jets are hidden. We show that
using suitable parameters, high-energy neutrinos in GeV - PeV range can be
produced in the hidden jet inside the collapsar, thus demonstrating that these
objects are candidates to produce neutrinos with energies between 1 - 10 PeV
which were observed with IceCube. On the other hand, due to matter effects,
high-energy neutrinos may oscillate resonantly from one flavor to another
before leaving the star. Using two (solar, atmospheric and accelerator
parameters) and three neutrino mixing, we study the possibility of resonant
oscillation for these neutrinos created in internal shocks. Also we compute the
probabilities of neutrino oscillations in the matter at different distances
along the jet (before leaving the star) and after in vacuum, on their path to
Earth. Finally, neutrino flavor ratios on Earth are estimated.
