Is it true that the market usually rises before the end of the year?
If so, why do you think it happens?
I spoke with few people that already said that in the last 5 years the market became really bulish
Yes, many people receive some money before the year ends and some would just like to invest it into something.
The opposite also holds true. By the end of the year people are willing to book profits and shell out on gifts and other things due to Black Friday, Christmas, New Year, and things like these. It is certainly possible that the December crash that started at the end of 2017 was because of these factors, that is people cashing out and wanting to spend cash in real life. That was a trigger that started off an avalanche of sell-offs that continued well into the first quarter of 2018. So don't dismiss the factor which works in the opposite direction as many people may be willing to disinvest by the year end.