I planted a young tree about a month ago but now there are small holes appearing and look like they arebeing eaten but I cant see any sign of a bug on there? Any thoughts please?

Are the holes at the edges of the leaves and look as though they have been nibbled? I had this with my witch hazel tree and the culprit was a leafcutter bee - fascinating to watch them at work and the tree is quite large so there were plenty of leaves left untouched.

yes looks like it. Its not a big tree though. That might explain why no caterpillars on it