What are the tree traversal methods?

from collections import deque

class TreeNode:
    def __init__(self, val, left=None, right=None):
        self.val, self.left, self.right = val, left, right

def inorder(node, out):
    if not node: return
    inorder(node.left, out)
    out.append(node.val)
    inorder(node.right, out)

def level_order(root):
    out, q = [], deque([root] if root else [])
    while q:
        node = q.popleft()
        out.append(node.val)
        if node.left:  q.append(node.left)
        if node.right: q.append(node.right)
    return out


# --- demo ---  tree:    4 / (2 / 1,3) , 6
root = TreeNode(4, TreeNode(2, TreeNode(1), TreeNode(3)), TreeNode(6))
out = []
inorder(root, out)
print(out)                 # [1, 2, 3, 4, 6]
print(level_order(root))   # [4, 2, 6, 1, 3]