title: How to create a js checkbox in flexdashboard? shinyTree does not work (R, shiny)
body: <p>I have a problem with using shinyTree in flexdashboard. In a regular shiny app works well:</p>
  <pre><code>library(shiny)
  library(shinyTree)
  server &lt;- function(input, output) {
    
    output$tree &lt;- renderTree({
      opciones = list('All'= list( 
        'Human' =  structure(list('OP1'='OP1', 'OP2'='OP2'),stopened=TRUE),  
        'Mouse' =  structure(list('OP3'='OP3'), stopened=TRUE)))
      attr(opciones[[1]],&quot;stopened&quot;)=TRUE
      opciones
    })
  }
  
  ui &lt;- fluidPage(
    shinyTree(&quot;tree&quot;, checkbox = &quot;TRUE&quot;)
  )
  
  shinyApp(ui = ui, server = server)
  </code></pre>
  <p>However, when I use it in Flexdashboard, it returns an empty tab (see this file: <a href="https://mega.nz/file/DCozwIiJ#ttcBe581FPfhINVoczfBvaXhgRlXwVSu-wd2JhXTEEY" rel="nofollow noreferrer">https://mega.nz/file/DCozwIiJ#ttcBe581FPfhINVoczfBvaXhgRlXwVSu-wd2JhXTEEY</a>)</p>
  <p>Do you have any idea why this could be happening and how to create a js tree checkbox in flexdashboard?</p>