reduce duplication

src/main.rs

@@ -60,15 +60,16 @@ where
 fn main() -> Result<(), Box<dyn std::error::Error>>{
     let cli = Cli::parse();
     let mut connection = Connection::new()?;
+    let tree = connection.get_tree()?;
 
     let node = match cli.use_field {
-        UseField::Class => find_node(&connection.get_tree()?, |node: &Node| {
+        UseField::Class => find_node(&tree, |node: &Node| {
             node.window_properties
                 .as_ref()
                 .and_then(|p| p.class.as_deref())
                 == Some(&cli.identifier)
         }),
-        UseField::AppId => find_node(&connection.get_tree()?, |node: &Node| {
+        UseField::AppId => find_node(&tree, |node: &Node| {
             node.app_id.as_deref() == Some(&cli.identifier)
         }),
     };