Trying to understand binary tree from array

leetcode/stdlib.py

@@ -1,6 +1,11 @@
 import typing
 
 
+class LinkedListNode(typing.Protocol):
+    val: int
+    next: typing.Optional["LinkedListNode"]
+
+
 class ListNode:
     """ListNode is the leetcode "standard library" type used in linked lists"""
 
@@ -9,8 +14,67 @@ class ListNode:
         self.next = next
 
 
+class BinaryTreeNode(typing.Protocol):
+    val: int
+    left: typing.Optional["BinaryTreeNode"]
+    right: typing.Optional["BinaryTreeNode"]
+
+
+class TreeNode:
+    """TreeNode is the leetcode "standard library" type used in binary trees"""
+
+    def __init__(
+        self,
+        val: int = 0,
+        left: typing.Optional["TreeNode"] = None,
+        right: typing.Optional["TreeNode"] = None,
+    ):
+        self.val = val
+        self.left = left
+        self.right = right
+
+    @classmethod
+    def from_int(cls, val: int | None) -> typing.Optional["TreeNode"]:
+        if val is None:
+            return None
+
+        return TreeNode(val)
+
+    # __repr__ was added by me
+    def __repr__(self) -> str:
+        filtered_parts = []
+
+        for key, value in [
+            ("val", self.val),
+            ("right", self.right),
+            ("left", self.left),
+        ]:
+            if value is not None:
+                filtered_parts.append((key, value))
+
+        middle = ", ".join([f"{k}={v!r}" for k, v in filtered_parts])
+
+        return f"TreeNode({middle})"
+
+    # __eq__ was added by me
+    def __eq__(self, other: typing.Optional["TreeNode"]) -> bool:
+        return (
+            other is not None
+            and self.val == other.val
+            and self.left == other.left
+            and self.right == other.right
+        )
+
+
+class ConnectableBinaryTreeNode(typing.Protocol):
+    val: int
+    left: typing.Optional["BinaryTreeNode"]
+    right: typing.Optional["BinaryTreeNode"]
+    next: typing.Optional["BinaryTreeNode"]
+
+
 class Node:
-    """Node is the leetcode "standard library" type used in binary trees"""
+    """Node is the *other* leetcode "standard library" type used in binary trees"""
 
     def __init__(
         self,