To add a treeview to a document library view, follow these steps:

  1. Browse to the view you want to add the treeview to. This must be a listview page (i.e. it won’t work on default .aspx or home.aspx).
  2. Edit the page in SharePoint Designer — then click Advanced Mode.
  3. Add a table to PlaceHolderMain with one row and two columns as shown below (NOTE: ” ”SharePoint doesn’t like these quotes. You need to change them all back to standard double-quotes " ".): 
    <table style="width: 100%">
<tr valign="top">
<td width="20%">
</td>
<td>
</td>
</tr>
</table>
  4. Move the existing Webpart Zone (the one that contains the view) and all its content to the second you just added.
  5. Add the following to the first you just added (the one whose width is 20%). Again make sure all the double-quotes get pasted properly! 
    <SharePoint:SPHierarchyDataSourceControl id="doclibDataSource" runat="server" RootContextObject="List" ShowFolderChildren="true" EnableViewState="false">
</SharePoint:SPHierarchyDataSourceControl>
<SharePoint:SPTreeView ID="doclibtreeview" runat="server" DataSourceID="doclibDataSource" EnableViewState="false" ExpandDepth="2" SelectedNodeStyle-CssClass="ms-tvselected">
</SharePoint:SPTreeView>

Save the page, and then view it in your browser

Reference link: http://www.nothingbutsharepoint.com/2012/10/22/add-a-treeview-to-a-document-library-using-sptreeview-and-sphierarchicaldatasource-aspx-2/

treeview