Bojan,
Interesting, if both spectra were taken with the same set-up - grating spacing/ camera etc. I'd expect the dispersion to be the same .....
The green dip is the "Canon" dip caused by the overlap of the Bayer filters in the DSLR camera. This can easily be compensated when doing the instrument response processing.
See the example "Astronomical Spectroscopy for Amateurs", p100.
Betelgeuse being a red giant M2/M3 has many Tio bands in the red.
Remember the Saha graph.
(
http://www.astronomicalspectroscopy.com/How_to.html)
This shows there is little possibility of Hydrogen in the spectrum.
The red dip looks to me like the pronounced Telluric band at 7600A, a good and easy marker....
EDIT: Looking at the MILES M2 reference...I had another go at re-calibrating (at 4.5 A/pix)