Every country spies on everyone else, including allies. But the extent and depth of Israeli spying in the U.S. is considered to be particularly extreme for allies. Importantly, there are rarely any repercussions, and Israel never cops to it, which is sort of a slap in the face.
When it was discovered that the U.S. was tapping Angela Merkel's cellphone there was public outrage in Germany, shock in the international community, and substantial consequences in terms of further reduced intelligence cooperation. It's worthwhile to mention that U.S. and German intelligence sharing is much more limited than between the U.S. and Israel, which is why Obama approved the tapping in the first place.
When U.S. espionage efforts in Japan were publicized, Obama ended up apologizing to Shinzo Abe.
AFAIK, the only other ally in recent U.S. history (past 50 years) that came close to the extent and depth of Israeli espionage is France. But nobody in the U.S. gave them a pass, either.
There are countless ways to distinguish Israeli efforts. Attempts to equivocate here basically amount to whataboutism. Until recently it would be hard to make strong value judgments because Israel is of course a sovereign nation with its own self interests, and their obnoxious spying seemed harmless enough considering they know how to keep a secret and were careful not to obstruct finalized Washington policy. But the problem with spying is that it can injure trust, and allies need to be able to trust each other as much as practicable. Now that Israel doesn't even pretend to be non-partisan wrt American politics, and even aggressively lobbied to kill the signed & sealed Iran nuclear deal, their efforts have arguably crossed a line even given the "special relationship" between the U.S. and Israel. (OTOH, I wonder which came first, the stingrays or Trumps public disclosure of secret Israeli intelligence. Perhaps Israel took the risk partly because of their distrust in Trump, either his honesty generally or at least his ability to keep a secret.)