The design of a tree, fundamentally, is both comically simple yet cleverly effective. You start with a thing. Call it the trunk. Make other ones of those on top of it. Maybe it looks like the letter Y. With one more little twist, you've finished the complex architecture of your organism: Repeat. Put the same Y on the tips of that Y, etc. Actually, there is one more twist: every once in a while, differentiate by specializing the next repeat.
Nature does well with repeats. It's no coincidence the vertebrae of the spinal column all look so similar. Nature makes this work because of the specialized differentiation that is the reason the pelvis happens to look like one of those vertebrae stretched out. It's the same reason the branching pattern continues in the leaves of a tree. But they're different enough to call them veins.
That's all we need to say about trees as in the plant. The tree just works too well in practically any context to limit ourselves there. We know what family trees are but do we ask why Nature bothered with this design? Why not make robust organisms who endure forever? Probably because that's a strategy that's not only doomed to failure but misses out on the benefits of a tree.
What a genius idea to make something last forever by embracing death instead. Let each generation make fresh copies of itself. Let those generations carry genetic experiments with them too. If over enough copying, the an experiment like fusing the ribs together in a shell proves beneficial, you'll make a turtle.
It's a design so good, it requires no maintainer. If a branch isn't strong enough to carry other branches, it won't. And there you have natural selection. That's a tree too.
I used to think I was clever to apply this wisdom by taking notes using a mind map, with bubbles and lines radiating out like a web. It's so much easier to follow the branches of a tree than simple notes. But then I realized, what is a bulleted list with nested bullets but the same thing laid out vertically? Bulleted lists are trees. Basically everything is a tree.
The trunk of the tree is "what it's all about". Everything that comes from it is a certified member but the trunk is a bold statement. It claims to be the basis of everything it connects to.
Then again, most trunks, well, almost exactly all trunks are by definition branches in disguise. A family tree is a pittance of the really tree, the cladogram of all life itself.
So there can only be one trunk in the end and this is what people mean when they ask "what is the meaning of it all?" The theory of everything, the root (the wrong term if you think in trees) of all that is everything.