can you put 2 tv antenna on the same mast for better reception?
You can't wire two antennas together because each antenna presents an impedance to the feed cable and TV that needs to be kept under control. Without controlled impedance matching you could end up with zero signal being received.

Therefore you can't just join up two antennas unless you really know what you are doing and of course there will be some losses that are inevitable. Those losses (even when you have done the best you can to match impedances and splice things together properly) might be enough to get really crappy reception from either antenna.

So it is best to use two antenna feed wires and have a selector box at the TV.

Regards having the two antennas close, this can cause other problems in that an antenna likes to have space around itself or the field patterns get disturbed. Again, a guy knowing what he is doing might be able to get the two antennas within a metre of each other but someone who doesn't know what they are doing is probably best to keep them as far apart as they can be and pointing in different directions.

Any radio antenna has a capture aperture (basically an area in square feet or sq metres) that is like the lens on a telescope - get in the way of that lens and you are reducing the signal. That aperture is usually a fair bit bigger than the mechanical dimensions of the physical antenna so this underpins what I said earlier - point them in different directions and keep them apart.