Very nice!

One minor point, the "/" in the 2nd equation "((4+c)*y)^(4+2)  /  5-s^200" gets a bit confused with the tree structure as you also use "/" to print the tree:

                       -
                    __/ \__
                   /       ^
                __/ \     / \
               ^     5   s   2
                   ^
                   ^
                   ^
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Maybe you could use "'/'" (that's a bit hard to read, here it is again with 4 spaces added: " ' / ' ") or similar to make it stand out a bit more:

                       -
                    __/ \__
                  '/'      ^
                __/ \     / \
               ^     5   s   2

                   ^
                   ^
                   ^
[download]

?