I know the topic is about the trees, but those buttons under the search box annoy me.
I think they take up too much space. How about two small buttons next to the search text box? Instead of "Next" and "Previous" the buttons could have left and right facing triangles.
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My example is ugly, but I'm hoping it illustrates my point. When the mouse cursor hovers over the buttons you could display a tool tip that says "Next" or "Previous" respectively.
Maybe the "Whole Word" and "Filter Tree" check boxes could be in a drop down menu from a third button next to the search text box.
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Seems cleaner and less cluttered to me, but that might be going too far.