pugixml not loading file

I'm trying to load "tree.xml" which is in the same directory as loadfile.cpp which also has pugixml.cpp, pugixml.hpp, pugiconfig.hpp.

#include "pugixml.cpp"
#include <iostream>
using namespace std;

int main()
{
    pugi::xml_document doc;

    pugi::xml_parse_result result = doc.load_file("tree.xml");

    if (doc.load_file("file.xml")){
        cout << "success" << endl;
    }else{
        cout << "fail" << endl;
    }

    cout << "Load result: " << result.description() << ", mesh name: " << doc.child("mesh").attribute("name").value() << endl;
}

and I get the result:

fail
Load result: No error, mesh name: 

I'm following manual here: http://ift.tt/1trtp15 under "Loading Documnet".

the tree.xml document looks like this:

<bookstore>
  <book category="COOKING">
    <title lang="en">Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <price>30.00</price>
  </book>
  <book category="CHILDREN">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
  <book category="WEB">
    <title lang="en">Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
  </book>
</bookstore>

Why isn't the file loading? I can't figure out wha'ts wrong.