ParseTree tree = parser.Parse("1 + 2"); ParseTreeNode node = tree.Root; ParseTreeNode leftChild = node.GetChild(0); AbstractSyntaxTree ast = leftChild.GetChildAst();In this example, we parse the expression "1 + 2" using a parser and retrieve its parse tree. Then, we navigate through the parse tree to retrieve the left child node, which corresponds to the number "1". We then use the GetChildAst method to retrieve the AST node that corresponds to the number "1". Package library: The ParseTreeNode.GetChildAst method is part of the Irony package library.