Oak tree growth

Oak tree growth

Observation - Oak tree growth - UK and Ireland. Description: This oak is in a pot in my garden. It has a lot of these berry like things on the underside of leaves and some on stems/twigs. The largest are about the size of a pea and in appearance look like unripe blackcurrants (without the little dry bit at the bott

This oak is in a pot in my garden. It has a lot of these berry like things on the underside of leaves and some on stems/twigs. The largest are about the size of a pea and in appearance look like unripe blackcurrants (without the little dry bit at the bottom). I've noticed there are some also on a large mature oak in my garden. I am assuming it is a caused by a parasite or insect. Any information appreciated.