  We present light curves and spectra of the tidal disruption event (TDE)
ASASSN-18pg / AT 2018dyb spanning a period of one year. The event shows a
plethora of strong emission lines, including the Balmer series, He II, He I and
metal lines of O III $\lambda$3760 and N III $\lambda\lambda$ 4100, 4640
(blended with He II). The latter lines are consistent with originating from the
Bowen fluorescence mechanism. By analyzing literature spectra of past events,
we conclude that these lines are common in TDEs. The spectral diversity of
optical TDEs is thus larger than previously thought and includes N-rich events
besides H- and He-rich events. We study how the spectral lines evolve with
time, by means of their width, relative strength, and velocity offsets. The
velocity width of the lines starts at $\sim$ 13000 km s$^{-1}$ and decreases
with time. The ratio of He II to N III increases with time. The same is true
for ASASSN-14li, which has a very similar spectrum to AT 2018dyb but its lines
are narrower by a factor of $>$2. We estimate a black hole mass of $M_{\rm BH}$
= $3.3^{+5.0}_{-2.0}\times 10^6$ $M_{\odot}$ by using the $M$-$\sigma$
relation. This is consistent with the black hole mass derived using the MOSFiT
transient fitting code. The detection of strong Bowen lines in the optical
spectrum is an indirect proof for extreme ultraviolet and (reprocessed) X-ray
radiation and favors an accretion origin for the TDE optical luminosity. A
model where photons escape after multiple scatterings through a super-Eddington
thick disk and its optically thick wind, viewed at an angle close to the disk
plane, is consistent with the observations.
