-# Node used in Tree implementation
-# nodes are used to store values
-# * `E`: type of value
-class TreeNode[K: Comparable, E]
+# Abstract node structure used in `Tree` implementation
+#
+# Nodes are defined recursively each node (except the root one) pointing to a parent.
+# Nodes can be used to store data with the `TreeNode::value` attribute.
+#
+# Formal parameters:
+# * `K`: key type (a `Comparable` one so nodes can be sorted by their keys)
+# * `E`: value type (to store your data)
+abstract class TreeNode[K: Comparable, E]