How to add multiple data to firebase and get them all in a list view

hi all , im trying to make an app which stores the list of the the students the names should be stored in firebase im trying the code with call data it is only storing one data like if im entering 1 it is stored as one but next time when i entered as 2 the first one is removed and 2 is only saved then i changed the store value block to append block it is showing a pop up like no previous values ..please help me

This may help with append values to list

ok thank you