Building xml tree (newbie quiestion)

help
1

Hi! I began to learn Rust and can't understand some basic principles.
I try to build xml tree. This is my main code
extern crate xml;

mod model;

use std::fs::File;
use std::io::BufReader;
use std::string::String;
use parser::xml::reader::{EventReader, XmlEvent};

pub fn build_tree(file_name: &String) -> model::Node {
    let file = File::open(file_name).unwrap();
    let file = BufReader::new(file);

    let parser = EventReader::new(file);
    let mut root = model::Node::new();
    let mut nodes = Vec::<&mut model::Node>::new();
    for e in parser {
        match e {
            c @ Ok(XmlEvent::StartElement { .. }) => {
                let mut new_node = model::Node::new();
                let add_node: &mut model::Node;
                {
                    add_node = match nodes.last_mut() {
                        Some(ref mut n) =>
                            n.add_child(new_node),
                        None =>
                            root.add_child(new_node)
                    };
                }
                nodes.push(add_node)
            },
            Ok(XmlEvent::EndElement { .. }) => {
                nodes.pop();
            },
            Err(e) => {
                println!("Error: {}", e);
                break;
            }
            _ => {}
        }
    }

    return root;
}

nodes is a vector contained nodes chain in depth. root - is a root node of tree. All nodes should be owned by root, but "nodes" should borrow links to nodes for find current node's parent.

And I get huge amount of borrow errors during compilation.

warning: unused variable: `c`
  --> src/parser/mod.rs:19:13
   |
19 |             c @ Ok(XmlEvent::StartElement { .. }) => {
   |             ^ help: consider using `_c` instead
   |
   = note: #[warn(unused_variables)] on by default

error[E0597]: borrowed value does not live long enough
  --> src/parser/mod.rs:24:30
   |
24 |                         Some(ref mut n) =>
   |                              ^^^^^^^^^ borrowed value does not live long enough
...
28 |                     };
   |                      - borrowed value dropped here while still borrowed
...
44 | }
   | - borrowed value needs to live until here
   |
   = note: consider using a `let` binding to increase its lifetime

error[E0499]: cannot borrow `nodes` as mutable more than once at a time
  --> src/parser/mod.rs:23:38
   |
23 |                     add_node = match nodes.last_mut() {
   |                                      ^^^^^ mutable borrow starts here in previous iteration of loop
...
44 | }
   | - mutable borrow ends here

error[E0499]: cannot borrow `root` as mutable more than once at a time
  --> src/parser/mod.rs:27:29
   |
27 |                             root.add_child(new_node)
   |                             ^^^^ mutable borrow starts here in previous iteration of loop
...
44 | }
   | - mutable borrow ends here

error[E0499]: cannot borrow `nodes` as mutable more than once at a time
  --> src/parser/mod.rs:30:17
   |
23 |                     add_node = match nodes.last_mut() {
   |                                      ----- first mutable borrow occurs here
...
30 |                 nodes.push(add_node)
   |                 ^^^^^ second mutable borrow occurs here
...
44 | }
   | - first borrow ends here

error[E0499]: cannot borrow `nodes` as mutable more than once at a time
  --> src/parser/mod.rs:33:17
   |
23 |                     add_node = match nodes.last_mut() {
   |                                      ----- first mutable borrow occurs here
...
33 |                 nodes.pop();
   |                 ^^^^^ second mutable borrow occurs here
...
44 | }
   | - first borrow ends here

error[E0505]: cannot move out of `root` because it is borrowed
  --> src/parser/mod.rs:43:12
   |
27 |                             root.add_child(new_node)
   |                             ---- borrow of `root` occurs here
...
43 |     return root;
   |            ^^^^ move out of `root` occurs here

I think I don't really understand borrow scopes. Can somebody explain? Or what it be useful to read?
Thank you!