Beetle attacking pear tree

The pear tree in our garden seems to be attacked by a beetle which bores holes into it. There are exit holes from the larvae and plenty of saw dust around it (see photos). As a result the leaves turn brown and curl up. (The bark of the tree appears white in the photos because we whitewashed it in an attempt to kill the beetles. We also had cut the tree to build a treehouse in it. The trunk is growing through the treehouse).What kind of beetle would you reckon it is and what would be the best kind of treatment?