  We propose novel tree level seesaw mechanism with TeV-scale vectorlike Dirac
mediators that produce Majorana masses of the known neutrinos. The gauge
quantum number assignment to the Dirac mediators allows them to belong to a
weak triplet and a five-plet of nonzero hypercharge. The latter leads to new
seesaw formula m_\nu ~ v^6/M^5, so that the empirical masses m_\nu ~ 10^{-1} eV
can be achieved by M ~ TeV new states. There is a limited range of the
parameter space with M < a few 100 GeV where the tree level contribution
dominates over the respective loop contributions and the proposed mechanism is
testable at the LHC. We discuss specific signatures for Dirac type heavy
leptons produced by Drell-Yan fusion at the LHC.
