That's a cool tree if it's real. If not a cool picture. I would think it would be like casting a Cholla Cactus only on a bigger scale, that is if your talking about casting it in one piece. If not I've cast Sequoia, which is the largest living thing on earth, with no problem. Back to your question if you want it in one piece I would think the hardest part would be mixing and stirring the resin!