What's my fruit tree called ?

difficult to say at the distance as you need to see aleaf/bark/branch to get an idea if its prunus/malus etc---
could be a crabapple golden hornet?

have you got crabs' crabapples that is I have seen yellow crabs' and the tree look like one

I'd hazard a guess that it is a malus, crab apple, but a close up pix. would help.

Are the fruits like apples or small plums? If like apples then the above answeres are likely; if like small plums then nice ripe greengages.

or even the yellow gage 'Oullins Golden'. Could also be the cherry plum 'Golden Sphere'. Definitely need a close up of the leaf and fruit.