Explain EXPLAIN AST (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 1)
    ExpressionList (children 1)
     Function tupleElement (children 1)
      ExpressionList (children 2)
       Literal Tuple_(UInt64_255, UInt64_1)
       Literal UInt64_1
