Young Birch tree issue?

Hello everyone.
3 years ago I planted a Birch - Betula Pendula. It had a lose plastic kind of coil wrap around the bottom to protect it. I removed this today and uncovered a load of ants and woodlouse.
The base is very rugged compared to the rest of the tree which has fine papery white bark. I am wondering if there is anything wrong with it.
It has great sentimental valuse as I bought it when my Nan died. It was 3ft tall when I bought it, it is now nearly 5 meters tall and looking lovely .... apart from its base!
Nothing rotting, wet or otherwise obvious, just what you see in the pics below
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These coil 'tree protectors' help to minimise damage from rabbits etc. ; they also provide cover for woodlice and other wood and bark devouring creatures . Despite the obvious damage to the bark , your tree has attained commendable proportions and looks quite healthy !
Birches are a very tough and hardy colonising genus of trees ; I wouldn't worry too much .