If you have lots of math expressions to write, you can use an infix reader in Common Lisp. It has a programmable reader. Such a thing - reading infix expressions - was already a standard feature of the MIT Lisp Machine OS in the 80s.

In Lisp you actually don't write parse trees. Lisp uses a serialized hierarchical data format of a tokenizer. S-expressions are not Lisp syntax trees, but a data format.