Explain EXPLAIN QUERY TREE (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 1)
     Function sum (children 1)
      ExpressionList (children 1)
       Function multiIf (children 1)
        ExpressionList (children 3)
         Function equals (children 1)
          ExpressionList (children 2)
           Identifier a
           Literal UInt64_1
         Literal UInt64_1
         Literal UInt64_0
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier m
