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