As simple as trimming a tree near live wires sounds, it is something that does require some thought before approaching the task.
Where HV wires are concerned, we would usually sleeve all of the wires with Neoprene sleeves along the length of the wires that may be contacted by a branch or other part of the tree.
Secondly, we'd use Hotsticks with a clamp on the end to pull the branch back so that it is nowhere near any lines, before it is cut.
All of the people involved in the trimming wear Insulated Gloves and Outers and also PPE related to the use of Chainsaws.