strang behavior of 2d array

Question

I creat a 2d array using two methods they look the same

helper1=[[]]*5
helper=[[] for i in range(5)]

when I append new element to the arrays, they behave differently

helper1[0].append(1) 
result is [[1], [1], [1], [1], [1]]
helper[0].append(1)
result is [[1], [], [], [], []]

I am surprised by the first outcome , why it is so? thanks !