The OP should explain how the measuring is done at the moment.
Trees tend to have branches which could make automated measurement very complex. But it is easy for a human brain to find a suitable work-around.
On a side note, this sounds like an attempt to replace a human with a machine. I think it is time we stopped doing that. It has been going on since the industrial revolution and, while it has made a few people very rich, it has not made humanity any happier.
...R