Important recent development in tree sitter was the new query language. Like TextMate or Sublime Grammars, ts in atom did use CSS selectors, but now it has a much more powerful s-expression query language which is useful for more than just syntax highlighting, e.g. static analysis. An application of that is Github's semantic, a haskell tool for code navigation and call graph analysis.
Demo and explanation: https://github.com/tree-sitter/tree-sitter/pull/444