from_json method to load tree from json.

treelib/tree.py

@@ -824,6 +824,26 @@ def to_json(self, with_data=False, sort=True, reverse=False):
         """To format the tree in JSON format."""
         return json.dumps(self.to_dict(with_data=with_data, sort=sort, reverse=reverse))
 
+    def from_json(self, json_str):
+        """
+        Load tree from exported JSON string.
+
+        :param json_str: json string that exported by to_json method
+        """
+        def _iter(nodes, parent_id):
+            for k,v in nodes.items():
+                children = v.get('children', None)
+                data = v.get('data', None)
+                if children:
+                    yield (k, data, parent_id)
+                    for child in children:
+                        yield from _iter(child, k)
+                else:
+                    yield (k, data, parent_id)
+
+        for i in _iter(json.loads(json_str), None):
+            self.create_node(i[0], i[0], parent=i[2], data=i[1])
+
     def update_node(self, nid, **attrs):
         """
         Update node's attributes.