How to write this kind of note?

See the section in the Handbook on tremolos: https://musescore.org/en/handbook/3/tremolo . Note that you need to use the advanced workspace. Follow the instructions here: https://musescore.org/en/handbook/3/tremolo#two_note. Then, to get them look like your example (which is now considered old-fashioned), select the tremolo mark itself and in the Inspector choose Tremolo>Style> Traditional.