# Get the node with the minimum key
	# O(n) in worst case, average is O(h) with h: tree height
	#
	#     var tree = new BinTreeMap[Int, String]
	#     for i in [4, 2, 1, 5, 3] do tree[i] = "n{i}"
	#     assert tree.min == "n1"
	fun min: E do
		assert not_empty: root != null
		return min_from(root.as(not null)).value
	end