When the Keep Tidy option in the Options menu is checked, the tree will be kept in an aesthetic arrangement. (The algorithm for this was written by Reingold & Tilford; see IEEE Transactions on Software Engineering 7 (1981).) This arrangement is probably the one you are familiar with from textbooks and class.
However, in the memory of a computer, the nodes are not kept in any special arrangement. They may be anywhere in memory, and only the pointers tie them together so you can get from one node to another. To get an idea of what this might look like if you could see into memory, choose Leave Natural. Now type in a tree. The nodes will be scattered in no particular pattern; yet, when you do a traversal, the computer has no problem following the links correctly to traverse the tree in the proper order.
