If you're keen, put this in a macro file and load it - function key F2 then gets you from the search box to the tree. It seems to work but don't blame me if it crashes one day...
#include "slick.sh"
defeventtab _options_tree_form;
void _options_tree_form.f2()
{
int treeWid = _find_control('_ctl_tree');
if (treeWid) {
treeWid._set_focus();
}
}