Nested dictionaries in Java

I'm finally almost done with my compression program, after six months! However, to finish I require nested dictionaries, which is like a dictionary returning dictionaries, which return more dictionaries, and so on. I need to have it like a tree, where I can add, remove, and edit "branches" of the nested dictionary tree at any time. The only solutions I see are one-time-only (you make the dictionary once, and then you never change it) and very complicated. Help, please!