Bugs on almond tree trunk

Hello from Greece...

We have an almond tree in our garden, and this year it seems that it has "adopted" a few thousand bugs that feed on the juice of the trunk by drilling with long thin tubes they insert in it (when I try to move them, it seems they are attached by their front part to the tree)...

They seem to excrete amounts of juice that attracts a lot of other insects, including wasps and flies... it also covers the area around the tree...

I have made some photos of them and will try to attach them...

Does anyone know what kind of insect it is ??