Yeah, good point. You could use std::vector or std::list. Under the hood those both use pointers, but kind of similar to how under the hood std::unique_ptr or std::box would use raw pointers.
In the specific case of a binary tree, where you only need left and right, std::vector/std::list would be overkill and slow down your program. But in a b-tree, std::vector would be good.
You can't use std::array or plain C arrays for the same reason you can't use raw values.
