It is not easy to tell a species from a simple picture ; It really helps if you can feel the leaf for thickness and whether it is in any way soft and can be compressed. I have a variegated Cornus that is very similar to your picture, There are also some variants of Beech that are similar. I also think it could be a variant Weigela as suggested.
I have some very strong cuttings that I am growing on, that I am not at all sure of, like yourself.
I will wait, as often the mature tree has slightly different leaves. That is IMO anyway.
Best of luck to you. It can be difficult ; you can send a leaf to various sites for identification. but it is not free..