Insert Attributes in Parent Nodes in JSON with data.tree in R

Question

I am new to tree.data, and have the following data:

library(data.tree)
library(jsonlite)

# data
Show <- c("The Flintstones", "The Flintstones", "The Flintstones","The Flintstones") 
Name <- c("Fred", "Wilma", "Barney", "Betty")
Status <- c("married", "married", "divorced", "divorced")
Sons <- c("Pebbles", "Pebbles", "Bamm-Bamm", "Bamm-Bamm")

# create dataframe
df <- data.frame(Show,Status,Name, Sons)

df
             Show   Status   Name      Sons
1 The Flintstones  married   Fred   Pebbles
2 The Flintstones  married  Wilma   Pebbles
3 The Flintstones divorced Barney Bamm-Bamm
4 The Flintstones divorced  Betty Bamm-Bamm

Now, I convert this dataframe in a Node object, without the SONS column which is added later as an attribute:

# create pathstring for node object WITHOUT the Sons column 

df$pathString <- paste(df$Show, df$Show, df$Name, sep = "/" )

# convert dataframe to tree.data 

flintStonesTree <- as.Node(df)

# show nodes

flinstStonesTree

# display node object
           levelName
1 The Flintstones    
2  °--The Flintstones
3      ¦--Fred       
4      ¦--Wilma      
5      ¦--Barney     
6      °--Betty 

Now, we grab this node object an convert it to to a list as an intermediate step to JSON, adding the SONS attribute in the node object with a function:

add_attr_function <- function(df, hierarchy_attribute = "level",
                              root = df$name, 
                              attribute = NULL)
  {
  # set hierarchy of node
  hierarchy <- unique(ToDataFrameTree(df, hierarchy_attribute)[[hierarchy_attribute]])
  
  # create JSON fields to extract
  jsonFields <- NULL
  
  # traverse tree
  t <- data.tree::Traverse(df, hierarchy_attribute)
  data.tree::Do(t, function(x) {
    x$attribute1 <- x[[attribute]] # add existing SONS attribute 
    })
  
  # add attribute to JSON
  jsonFields <- c(jsonFields, "attribute1")
  
  if(is.null(jsonFields)) jsonFields <- NA
  data <- data.tree::ToListExplicit(df, unname = TRUE, keepOnly = jsonFields)
  x1 <- list(data = data)
  
  # return list for further JSON transformation 
  return(x1)
  
} 

# run the function and adding SONS attribute
list_with_added_attr <- add_attr_function(flintStonesTree, attribute = "Sons")

# transform the list to JSON
convert_to_json <- toJSON(list_with_added_attr, auto_unbox = T, json_verbatim = TRUE)

# output with SONS added to very child of the tree

{
  "data": {
    "name": "The Flintstones",
    "children": [
      {
        "name": "The Flintstones",
        "children": [
          {
            "name": "Fred",
            "attribute1": "Pebbles"
          },
          {
            "name": "Wilma",
            "attribute1": "Pebbles"
          },
          {
            "name": "Barney",
            "attribute1": "Bamm-Bamm"
          },
          {
            "name": "Betty",
            "attribute1": "Bamm-Bamm"
          }
        ]
      }
    ]
  }
} 

The question : I managed my way to add attributes to children but unable to parent nodes. How can I do it?

Thanks in advance.