That was my first thought too. Debra Butterfield has worked in stick and mud, and then found wood often cast into bronze so the sculpture can exist in outdoor settings. When you look at her bronze horses, it is difficult to accept that the pieces are bronze and not wood.
Artists ‘build’ trees all the time. A truly tree house worthy sculpture is Ai Weiwei’s “Iron Tree”. Massive and strong enough to support a tree house.