If the data source has serverPaging enabled the TreeList control doesn't create a pager. Created a dojo thing to replicate, un-comment the serverPaging data source configuration to cause the pager to stop being created.
At this point the TreeList supports only client side paging. You can test it in the following demo:
In the above sample you can also see how does the TreeList handle groups which are split by the page - it renders the rest of the items on the next page.