An unknown guest on my oak

This tree has grown close to one of my oak.

Do you know what kind of tree this could be ?
It has little white spots on a brown bark.

If it's an "interesting tree", I will do an air layer to place it somewhere else.

Thank you ;-)

 

Hi Andre, could it be an Elderberry, Sambucus ?

 

I don't think so because elderberry has grey green bark and this one is deep brown.

 

Hmmm, Maybe a photo of the buds or leaves will help.

 

Sure, I'll post one in a few weeks when the leaves will show up.

 

Looks similar to a hazelnut or birch, Betulaceae family.

 

Here are the leaves, I think it's Rhamnus frangula. What do you think ?

 

I agree, both bark and leaves looks like Rhamnus frangula.