<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def find_focusable(node):
 """ Search for the first focusable window within the node tree """


    if not node.children:
        return node

    if node.focus:
        return find_focusable(node.children_dict[node.focus[0]])