Minecraft Tree house/underground base

in my inecraft base its for my server and my faction. So basically a giant hollow tree with a mineshaft entrance in its trunk, along with some space for various things, remember mods installed. So the hollow tree has floors on the inside. Also its surrounded by a water moat on one side and the ocean on the other. The underground bit connects to a underwater piece as well. The underground part of the base streches into y=11 and x plus z is unknown to me. So i guess you could say i am reaching into a fuggy idea that keeps upgrading this ideal of mine.