unknown insect-caused growth???

unknown insect-caused growth???

Observation - unknown insect-caused growth???. Description: 2mm - 4mm high perpendicular growths on beech leaves on a young beech tree in urban woodland. Some leaves had four or five of these. The growths were pale at the bottom, green higher up, and were bristly rather than smooth in appearance

2mm - 4mm high perpendicular growths on beech leaves on a young beech tree in urban woodland. Some leaves had four or five of these. The growths were pale at the bottom, green higher up, and were bristly rather than smooth in appearance