Questions about programming related to a regular binary tree, Stopwatch'er and self-test.?

Question

Algorithms

Good afternoon, Khabrachan! I need your help in understanding some aspects. Here are the questions that I had while studying Stopwatch and binary trees:
1. What is the "error" of Stopwatch'er when measuring the execution time, for example, of some piece of code? After all, there are checks in Stopwatch'er.
2. I know what a binary search tree is, what it is for, when it is used, etc... But... what are ordinary binary trees for? What are their rules for adding a new element, if in a binary search tree, if this element is less than the element with which it is compared, then it goes to the left, and if more, then to the right?
3. Habrachans, can you please come up with questions for me to self-test on binary trees (both search and ordinary)? And then I have the feeling that I didn’t understand something or don’t know, although, it seems, when I was sorting out the binary search tree, I understood everything well. Emphasis in self-examination, I would like to theory. Or, as an option, tell me where I can test my theoretical knowledge of binary trees, please.