First introduced when Thor draws it for Jane Foster to explain the nine realms, it also shows up several more times.

The most notable is in Captain America: The First Avenger, when it’s engraved into the wall where the Red Skull finds the Tesseract. Later, it’s seen carved in the wooden door of the safe house in Ragnarok, where Heimdall is hiding the Asgardians from Hela.

At the end of the film, a similar tree can be seen burning in the middle of Asgard, as a sign of dangerous things to come to the nine realms.