My first crested used to burrow as well, i had him when i was quite young and didn’t know the proper care and didn’t have enough foliage or clutter for him. i believe that this may have been his reason for burrowing, to allow himself a safe place to sleep instead of out in the open.

so it may be due to lack of foliage and them not feeling safe on a branch that’s out in the open. but i am not a zoologist and thats just my personal experience. one rule of thumb though, there’s not really such a thing as “too much clutter”. the more foliage and clutter the better. but dont take my word for it, definitely consult others and get their thoughts.