shinyTree Checkboxes using Dates

I'm trying to create a branching checkbox input using dates similar to the picture below.

The final selections will be unique observations from the prior selected Name. Each Name could have many observations so I'd like to be able to use dates to choose specific ones. An example of my current code is below. I'm able to update the checkbox input based on the name to show all the Name's observations.

ui.r

library(shiny)
library(dplyr)

shinyUI(
    fluidPage(
        navbarPage(inverse = TRUE,
                   tabPanel("Page Title",
                            sidebarPanel(width = 4,
                                         selectizeInput("Name",
                                                        label = "Name",
                                                        choices = sort(unique(mydata$Name))
                                         ),
                                         checkboxGroupInput("Observation",
                                                            label = "Observation",
                                                            choices = sort(unique(mydata$Observation))
                                         )
                            )
                            ,
                            mainPanel(
                                tableOutput("RepDimTable")
                            ))
                   
        )))

server.r

library(shiny)
library(dplyr)

shinyServer(function(input, output, session){
    
    dat <- reactive({
        
        d <- mydata %>%
            filter(Name == input$Name)
        
        updateCheckboxGroupInput(session, "Observation", choices = unique(d$Observation))
        
        d
        
    })
    
    
    output$RepDimTable = renderTable({

        repDimReactive = dat()   %>%
            filter(Observation %in% input$Observation) %>%
            select(Observation, Date, Name, Colour, Score)
        
        repDimReactive
        
    })
})

I'm unsure how to create the branching checkbox from the Date and Observation columns. I've attempted shinyTree solutions but didn't know how to nest the dates and observations into a useable list form.

Data

mydata <- structure(list(Observation = 1:8, Date = c("2020-12-01", "2020-12-01", 
"2020-12-01", "2021-01-01", "2021-01-01", "2021-01-01", "2021-01-15", 
"2021-01-15"), Name = c("Bob", "Fred", "George", "Bob", "Bob", 
"George", "Fred", "George"), Score = c(1L, 4L, 1L, 2L, 2L, 3L, 
2L, 1L), Colour = c("Red", "Blue", "Blue", "Green", "Blue", "Blue", 
"Green", "Red"), Year = c(2020L, 2020L, 2020L, 2021L, 2021L, 
2021L, 2021L, 2021L), Month = c(12L, 12L, 12L, 1L, 1L, 1L, 1L, 
1L), Day = c(1L, 1L, 1L, 1L, 1L, 1L, 15L, 15L)), row.names = c(NA, 
8L), class = "data.frame", na.action = structure(9:22, .Names = c("9", 
"10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", 
"21", "22"), class = "omit"))