I have two arrays:

a = [1,2,3]
b = [4,5,6]

I'd like to insert b at index 1 of a, to have :

c = [1,4,5,6,2,3]

Is there a builtin function to do this ? I found the answer for a single element, but not for a whole array. I imagine something like concat but with an additional parameter which would be the index of insertion.