Explain EXPLAIN SYNTAX (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 1)
     Function plus (alias a) (children 1)
      ExpressionList (children 2)
       Literal UInt64_1
       Literal UInt64_1
    ExpressionList (children 1)
     Identifier a