I believe you're using Visual C++. My suggestion is to create a new project and add your files again to see if you run into the same error. Essentially, your errors are stating that all of your class functions have already been defined and you're simply trying to redefine them. This usually comes from 1) MSVC messing up (happens a lot) 2) you are #include'ing your tree.cpp along with compiling it, or 3) you have copied the function definitions elsewhere in your code.
It's hard to say specifically what's causing the problem, but I'd start with my suggestion and if that doesn't work, I suggest copy/pasting each file here and include the name of the file as well.