Wrong product recommened

On Sunday I went to Lifestyle Garden Centre to get an insecticide 'Fungarid' for my indigenous tree, which flower and fruits. The ladies at information referred me to a young gentleman that works for Efekto. Patiently he listened to my problems and saw the photos too. There wasn't a product like 'Fungarid' and he said my tree needed something and carbon. He then recommend I use 'Wonder Lawn & Leaf 7:1:3 (15) + C (8) SR* which I purchased. He also said he hasn't worked with fertilisers for some time, yet he gave me this product and I trusted him. After doing research I found that this product is for maintaining a healthy lawn and non-flowering shrubs and foliage. What if I used this product without getting more information, my poor tree. Now I have a product which I won't be using.