通过LINQ向树添加节点会在运行时创建“不支持查询运算符”

I am trying to get my head around a LINQ issue. The ultimate goal is to load tree view with data acquired from LINQ to SQL (view). The issue is when I try to access the data acquired it keeps throwing a "query operator not supported during runtime". The code involved is no more than:I am trying to get my head around a LINQ issue.