The tree node has a fixed height. You can't break the node text. The alternative solution to solve this issue is to limit the node width and show a tip message when hovering this node.
<li>
	<div title="Create_New_BOM_SOP____AAAAAAAAAAAAAhdfhdsfhjse" style="max-width:100px;overflow:hidden;text-overflow: ellipsis">Create_New_BOM_SOP____AAAAAAAAAAAAAhdfhdsfhjse</div>
</li>
Also, you can use the treegrid instead, which has 'nowrap' property that allows you break a line in a node.