What is the syntax to insert one list into another list in python?

Given two lists:

x = [1,2,3]
y = [4,5,6]

What is the syntax to:

1. Insert x into y such that y now looks like [1, 2, 3, [4, 5, 6]]?
2. Insert all the items of x into y such that y now looks like [1, 2, 3, 4, 5, 6]?