Create a square of increasing size by replicating the initial code
Pyth, 2 bytes


5


Try it online! Also Try it doubled, tripled!

How does that work?

\n is the command that prints its argument with a trailing newline, while returning it simultaneously. So, each time you make an insertion, you turn the integer literal 5 into a number containing N copies of 5 concatenated, and the leading newlines basically make sure it's printed the appropriate number of times, thus keeping it square.