Immediate Help - Citrus Tree Branches Slowly Drying Out
Hello everyone,
My potted mandarine tree has started developing dead/drying branches mostly from the upper parts of the tree, and it seems to slowly spread branch by branch. Some leaves dry out and curl, while other parts of the tree are still producing healthy green new growth.
It is currently on a closed balcony but It was inside by a large window until very recently. I moved it to balcony thinking it would help with the situation. I dont use any fertilizers and only water it. I repotted it from a 10L to a 20L last summer but roots were not crammed back then. I am trying to water it by checking the soil but I am not sure if I was giving enough each time.
I feel very lost and stressed, because I dont want this tree to wither, I planted it from a seed and it has been with me since then and I am very attached to it. I would really appreciate any help identifying whether this looks more like underwatering/root stress, environmental stress, or disease, and what my best next steps should be.
I am a student therefore I did not plant it, I really want to understand what I need to do to save it, so please excuse me if this is not the ideal subreddit or if I am breaking any rules here.
note: It is from a mandarin seed and I am not sure what to call it since it is not grafted.
I am attaching an earlier photo at the end.