@Gustavo Martins your tree looks like it was started as an air layer. When air layering maples--especially those that callus aggressively--you can expect it to form 'hips' at the nebari, like your tree has done. These hips are more apparent if the roots are initially allowed to grow vertically (downward) like yours, as opposed to using a disk when air layering to redirect the roots horizontally.
I start a lot of air layers, and see these 'hips' on a regular basis. It is easier to correct this earlier rather than later in the tree's life. I attached an image of an air layer that was started 21 years ago by David Easterbrook. As you can see, this problem does not correct itself over time. This tree has been in my garden since 2019, and i'm actively working on fixing this by using a board and a fairly large training pot (next year, a box). I also identified a leader that will be allowed to extend freely to add girth to the trunk.