SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function nested (children 1)
     ExpressionList (children 3)
      Literal Array_[\'a\', \'b\']
      Function materialize (children 1)
       ExpressionList (children 1)
        Literal Array_[UInt64_1, UInt64_2]
      Function materialize (children 1)
       ExpressionList (children 1)
        Literal Array_[UInt64_3, UInt64_4]
