Thanks to War History Online I am now aware that fake trees were used in WW1. Not sure I would liked to be the person who has to be stuck inside one when it was behind enemy lines! Did they use a radio to send back intelligence? As you see the entrance to the tree was under ground level and normally well covered up.
Allied soldiers discover a fake tree entrance hole. You can see the huge stump next to this too, most probably planted in a large wood before bombs decimated the rest of the real trees. You just have to see Flanders fields to know what they ended up like.
Original drawing plans for fake trees. Right hand one in water location?