Where does “tryg” come from?

tryg (Middle English) comes from Old Norse tryggr, from Proto-Germanic triwwiz, from Proto-Indo-European drew-, from Proto-Indo-European dóru, from Proto-Indo-European deru- — firm, solid; wood; be firm, hard, solid.

Ancestry of “tryg”, step by step

Step	Language	Word	Meaning
1	Old Norse	tryggr	true
2	Proto-Germanic	triwwiz	true; faithful
3	Proto-Indo-European	drew-	hard, firm, strong, solid; hard, fast; tree
4	Proto-Indo-European	dóru	tree
5	Proto-Indo-European	deru-	firm, solid; wood; be firm, hard, solid

Every word from Proto-Indo-European deru- →Every word from Proto-Indo-European drew- →Every word from Proto-Indo-European dóru →