Tooltip for the SearchIcon in TreeRoot is not possible

**Describe the bug**
We want to add a tooltip to the searchicon of the TreeRoot. The Problem is that we only get the searchicon when the search is initialized as well -- which is only done in the clickhandler of the searchicon.
So it would be great if the search is implicitly initlaized when setSearchable() is executed or if there would be any way to get the search to do it manually.