如何在ICollection中将项添加到特定索引中？

Code:

码：

TestItem TI = new TestItem();
ITestItem IC = TI;
controls.TestItems.Add(IC); //This adds the item into the last column, but I need to add this in a particular index

TestItem is a Class  
ITestItem is an Interface 
controls is a local variable
TestItems is a ICollection<ITestItem>
TestItem TI = new TestItem();
ITes