Inserts an array of items into the LeadCollection at the specified index.
index
The 0-based index at which items should be inserted.
items
An array of items to insert. Items may be null.
InsertRange internally calls InsertItemRange, which may be overriden.
LeadCollection accepts null as a valid value and allows duplicate items.
If index is equal to Count, items are added to the end of LeadCollection.
This method raises the CollectionChanged event with the Add action.