fix: apply code review suggestion

tree/item.go

@@ -53,7 +53,8 @@ func NewStringData(data ...string) Data {
 
 var _ Data = NewFilter(nil)
 
-// Filter applies a filter on some data.
+// Filter applies a filter on some data. You could use this to create a new 
+// tree whose values all satisfy the condition provided in the Filter() function.
 type Filter struct {
 	data   Data
 	filter func(index int) bool