clear
add 2
add 1
add 4
add 3
add 5
print
level 0: 2(3)
level 1: 1(1) 4(2)
level 2: 3(1) 5(1)
remove 1
print
level 0: 4(3)
level 1: 2(2) 5(1)
level 2: 3(1)