Currently there is no client side API to bind data from client side. Please add this feature.

ADD: Functionality in TreeList to Sorting with Subobjects like this:

<telerik:TreeListBoundColumn DataField="subobject.MyPropertyName" SortExpression="subobject.MyPropertyName"
 HeaderText="MyPropertyName" UniqueName="MyPropertyName"  >
        

Workaround would be to apply the first-column indicator CSS class name in the markup. Then this class name will be inherited by the next column if the first is Hidden.

With the following markup, the rendered results, the "Parent Category ID" column header will have the "first-visible-column" CSS class name set.
<telerik:TreeListBoundColumn DataField="ID" UniqueName="ID" HeaderText="Category ID" Visible="false">
    <HeaderStyle CssClass="first-visible-column" />
</telerik:TreeListBoundColumn>

<telerik:TreeListBoundColumn DataField="ParentID" UniqueName="ParentID" HeaderText="Parent Category ID">
</telerik:TreeListBoundColumn>
OR

If applying in the Code Behind, try using the PreRenderComplete event of the Page.

protected void Page_PreRenderComplete(object sender, EventArgs e)
{
    string firstVisibleColName = RadTreeList1.RenderColumns.Where(x => x.Visible && x.Display).First().UniqueName;

    TreeListHeaderItem headerItem = RadTreeList1.GetItems(TreeListItemType.HeaderItem)[0] as TreeListHeaderItem;
    headerItem[firstVisibleColName].CssClass += " first-visible-column";
}

The agregate sum value shown in the bottom of the TreeList columns displays bigger sum than the actual one (it seems that the child items values are also taken into consideration).

Steps to reproduce:
1. Open http://demos.telerik.com/aspnet-ajax/treelist/examples/columns/aggregates/defaultcs.aspx?show-source=true

2. Check the sum shown in the Population column

Actual: It shows 10,702,470,081.00

Expected: It should be 6,464,732,588.00

This functionality would aggregate a lot of value to the RadTreeList.  I will explain you why it is important. In order to prepare the information to give it to the TreeList, it is necessary to make a lot of hierarchical calculations that consume a lot of CPU and memory resources.  It causes that any server could be busy doing the same complex calculations with each click expanding any level. If you have a lot of users that expands a node of the tree, the server could crash. I prefer,  RadTreeList had all the information one time to prevent making unnecessary recalcularions with every click. 

I like Telerik components, but this issue make me to search another tree component in the market.  Please reconsider this functionality in your next version of your RadTreeList.

RadTreeList control dose not support RTL format, please add this feature.

check attachement.

Your RadTreeList for ASP.NET AJAX is an amazing product but we would love to see more of the grid functionality implemented in it.

Two very notable features from the RadGrid we would like to have in the RadTreeList are the "EnableHeaderContextMenu" so that we can hide and show columns on-demand and also column filtering capability.

Please think about including these in future releases.

Thanks,
Curtis

When using LoadOnDemand in a RadTreeList, it would be great to have it automatically expand to a selected item when initially loading on a page.

Allow client side expand/collapse for RadTreeList