  Fermi line of bilayer graphene at zero energy is transformed into four
separated points positioned trigonally at the corner of the hexagonal first
Brillouin zone. We show that as a result of this trigonal splitting the minimal
conductivity of an undoped bilayer graphene strip becomes anisotropic with
respect to the orientation $\theta$ of the connected electrodes and finds a
dependence on its length $L$ on the characteristic scale $\ell=\pi/\Delta
k\simeq 50 nm$ determined by the inverse of k-space distance of two Dirac
points. The minimum conductivity increases from a universal isotropic value
$\sigma^{min}_{\bot}=(8/\pi)e^2/h$ for a short strip $L\ll \ell$ to a higher
anisotropic value for longer strips, which in the limit of $L\gg \ell$ varies
from $(7/3)\sigma^{min}_{\bot}$ at $\theta=0$ to $3\sigma^{min}_{\bot}$ over an
angle range $\Delta \theta\sim \ell/L$.
