我无法在shinydashboard中放置更多menuItem()

library(shiny)
library(shinydashboard)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(
    sidebarMenu(
      menuItem("主页", tabName = "home", icon = icon("home")),
      menuItem("子菜单", icon = icon("th"),
               menuSubItem("菜单项1", tabName = "item1"),
               menuSubItem("菜单项2", tabName = "item2"),
               menuSubItem("菜单项3", tabName = "item3"),
               menuSubItem("菜单项4", tabName = "item4"),
               menuSubItem("菜单项5", tabName = "item5")
      )
    )
  ),
  dashboardBody(
    tabItems(
      tabItem(tabName = "home",
              h2("主页内容")
      ),
      tabItem(tabName = "item1",
              h2("菜单项1内容")
      ),
      tabItem(tabName = "item2",
              h2("菜单项2内容")
      ),
      tabItem(tabName = "item3",
              h2("菜单项3内容")
      ),
      tabItem(tabName = "item4",
              h2("菜单项4内容")
      ),
      tabItem(tabName = "item5",
              h2("菜单项5内容")
      )
    )
  )
)

server <- function(input, output) {}

shinyApp(ui, server)