How to make column read only in xtratreelist in windows form

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C#

DevExpress

I fetch the data's form data base and bind it in treelist .I would like to make some of the columns as read only property.I can do read only rows in a treelist.but i can't do the same process for column.

What I have tried:

using DevExpress.XtraTreeList;

 private void treeList1_ShownEditor(object sender, EventArgs e)
        {
            if (((TreeList)sender).FocusedNode[colname].ToString() == "aa") 
                ((TreeList)sender).ActiveEditor.Properties.ReadOnly = true;
        }