Considering you have file that contains various file paths as comma delimited strings as input. Example - ``` a,b,c,d,e,g a,d,f,e,r b,t,y,a,r ``` Each line represents a path. Assume that there is folder b and d inside a and then folders are further nested inside both b and d too. The task is to prepare a UI where we should have a dropdown listing down the first level of folders and as you make a selection, more dropdowns should appear to choose the folders from available options at each nested level. This should happen really efficiently with zero lag. These strings can have millions of values with billions of such strings.