Inserts an item into the LeadCollection at the specified index.
index
The 0-based index at which item should be inserted.
item
The object to insert. The value can be null.
InsertItem is meant to be overridden in a derived class. For a public method to insert an item in the LeadCollection, see Insert.
LeadCollection accepts null as a valid value and allows duplicate items.
If index is equal to Count, item is added to the end of LeadCollection.
This method raises the CollectionChanged event with Add action.
Notes to Inheritors
Derived classes can override this method to change the behavior of the Insert and Add methods.