I thought you might be in the UK...first thing to say is your tree is planted much too close to the fence behind it, unless, that is, it's Prunus amanogowa, the flagpole cherry. Second, I suspect it has Cherry Leaf Spot (see here https://www.rhs.org.uk/advice/profile?PID=567) especially if its shedding leaves early. Third, it appears to have been attacked or used by leaf cutting bees, or possibly vine weevil - at the top of the tree, there seem to be notches rather than semi circular bits missing at the leaf edges. If its leaf cutting bees, there's not much you can do about that, and they will have stopped cropping the leaves by now anyway - they crop semi circles from leaves and roll them to rear their young, because they're solitary bees. If there are notches, as it looks to be, then I'd suspect vine weevil, and a soil drench with nematodes might be necessary, but another photo of those leaves at the top will confirm or deny.
Finally, it really doesn't look too well - if you didn't improve the soil prior to planting by digging in composted manure or your own good garden compost, or some other organic soil conditioner, then it looks like it needs some help. If you didn't prepare the area in this way prior to planting, then, if possible, I'd dig it up (provided it really hasn't been in place more than 2 years), carefully extracting the long roots which will have spread out not far under the surface, as well as the other roots which go straight down, lay it down somewhere and cover the roots with a tarpaulin, out of the sun, then dig the area over properly, incorporating organic material, and replant at least 2 or preferably 3 feet away from that fence. If you do this, it's important to shape the planting hole in such a way that the roots can be put into the soil without cramping or bending them, and this job would be best done in late October.
Alternatively, it's far too late in the year to give it any fertilizer, but you could mulch it with composted manure, taking care not to let it sit against the trunk of the tree. If it has got leaf spot, do not allow any fallen leaves to remain on the ground for any longer than necessary, and certainly remove all fallen leaves once they're all on the ground.