  We measured the spectrum of a single-carrier bilayer graphene quantum dot as
a function of both parallel and perpendicular magnetic fields, using a
time-resolved charge detection technique that gives access to individual tunnel
events. Thanks to our unprecedented energy resolution of 4$\mu~$eV, we could
distinguish all four levels of the dot's first orbital, in particular in the
range of magnetic fields where the first and second excited states cross
($B_\perp\lesssim 100~$mT). We thereby experimentally establish, the hitherto
extrapolated, single-charge carrier spectrum picture and provide a new upper
bound for the inter-valley mixing, equal to our energy resolution.
