Explain EXPLAIN SYNTAX (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 2)
   SelectQuery (children 2)
    ExpressionList (children 1)
     Literal UInt64_1 (alias x)
    ExpressionList (children 1)
     Identifier x
   SelectQuery (children 2)
    ExpressionList (children 1)
     Identifier x
    ExpressionList (children 1)
     Literal UInt64_1 (alias x)
