Add docs for topic "cst"

Author: shaedrich

topics/cst/index.md

@@ -0,0 +1,12 @@
+---
+created_by: 
+display_name: Concrete syntax tree
+released: 
+short_description: A concrete syntax tree is an ordered, rooted tree that represents the syntactic structure of a string according to some context-free grammar.
+topic: cst
+aliases: parse tree, parsing tree, derivation tree
+url:
+wikipedia_url: https://en.wikipedia.org/wiki/Parse_tree
+related: ast
+---
+A concrete syntax tree is an ordered, rooted tree that represents the syntactic structure of a string according to some context-free grammar.