R shinydashboard collapsible menuItem with inputs

Question

I am trying to implement a fileInput using library(shinydashboard) to provide the user with the option to upload files (as it was done here with a basic shiny UI - please find the example code below).

I would like to place the fileInput in the dashboardSidebar in an expandable menuItem, but don't know where it should go into the shinydashboard structure.

library(shiny)

ui <- fluidPage(
  titlePanel("Uploading Files"),
  sidebarLayout(
    sidebarPanel(
      fileInput("file1", "Choose CSV File",
                multiple = TRUE,
                accept = c("text/csv",
                           "text/comma-separated-values,text/plain",
                           ".csv")),
      tags$hr(),
      checkboxInput("header", "Header", TRUE),
      radioButtons("sep", "Separator",
                   choices = c(Comma = ",",
                               Semicolon = ";",
                               Tab = "\t"),
                   selected = ","),
      radioButtons("quote", "Quote",
                   choices = c(None = "",
                               "Double Quote" = '"',
                               "Single Quote" = "'"),
                   selected = '"'),
      tags$hr(),
      radioButtons("disp", "Display",
                   choices = c(Head = "head",
                               All = "all"),
                   selected = "head")
    ),
    mainPanel(
      tableOutput("contents")
    )
  )
)

server <- function(input, output) {
  output$contents <- renderTable({
    req(input$file1)
    df <- read.csv(input$file1$datapath,
                   header = input$header,
                   sep = input$sep,
                   quote = input$quote)
    if(input$disp == "head") {
      return(head(df))
    }
    else {
      return(df)
    }
  })
}

shinyApp(ui, server)