Please help me with my Christmas tree

thank you for giving the time to read my problems i am having. any help will be greatly appreciated. 

i have a christmas tree that is my daughters first christmas tree she got when she was 6 months old. it lived and i have been keeping it in a pot and getting bigger pots for it so it can grow.

i really want to keep the tree and make it last. last year i noticed the tree had clear bugs over it and ants all over it. i poured listening moth wash over which killed all the bugs but turned tree white. i rinsed it off and all seemed fine. now worried as pine needles are going black as like its coated in something. perhaps a fungus. also some small black bugs on it. some needles are going brown and ends of some branches and brown dry and hard and have died. but new shoots have opened and still growing but some have gone brown and died whilst they were growing. i will get some ups for you. any advice for treatment and plant food.