how to add custom bullets in tinymce 3.x

Question

i want to add custom bullet points in my tinyMCE editor 3.x.

i have done.

advlist_bullet_styles:
[
{
title:'image bullet',
styles:{
listStyleImage:"URL('URL of image')"
}
}
],

but it not working it shows by default disc bullet and console have no error regarding image not found. please anyone knows how to add custom bullets. please help me.