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

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

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

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.

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.

This error occurs using version 2013.2.717.45 of Telerik.Web.UI.dll

We are using a RadTreeList to display data with a three-part key.  The control was set up with AllowLoadOnDemand="true", DataKeyNames="Key1,Key2,Key3", and ParentDataKeyNames="ParentKey1,ParentKey2,ParentKey3", and both the NeedDataSource and ChildItemsDataBind events were handled properly on the server side.  Clicking the expand/collapse buttons resulted in erratic behavior -- sometimes, all nodes on a given level would be expanded or collapsed at once, sometimes, the entire tree would collapse and not be able to be expanded again, and occasionally the desired node would expand or collapse as desired.

I tracked the problem (using JustDecompile) to a bug in TreeListLoadOnDemandContext.ItemNeedsToBeExpanded.  The same bug appears to be in ItemNeedsToBeSelected, RemoveExpandedDataKeyValue, and RemoveSelectedDataKeyValue as well.  In all four cases, the code loops through the data keys comparing one to the next -- but overwrites its flag on each iteration.  In other words, it doesn't check if ALL keys are equal, only if the last one compared is equal.


I added "Key" and "ParentKey" fields to the data object that combined all three fields into a single struct, so that the control now has DataKeyNames="Key" and ParentDataKeyNames="Parent", and it now works properly.

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

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