python loop x + 1 times in a list of list until number y

What I want is the list in num loops x + 1 everytime until y is generated(and loops is stoped), which is a large number.

num = [[1], [2,3], [4,5,6], [7,8,9,10], ... ,[... , y]] 

# something like[[1 item], [2items], [3items], ...]
# the number append to the list can be a random number or ascending integers.