Red growth on tree

Red growth on tree

Observation - Red growth on tree - UK and Ireland. Description: Small 8mm tall red spines, sticking up from leaf. Not sure what type of tree it is. The leaves as far as I could see were covered in these small red spikes, some leaves had up to 30 spikes closely growing together, is this an insect egg? or some sort of

Small 8mm tall red spines, sticking up from leaf. Not sure what type of tree it is. The leaves as far as I could see were covered in these small red spikes, some leaves had up to 30 spikes closely growing together, is this an insect egg? or some sort of fungus?