added a intermediate category and added binary tree concept

Author: W-ight

dsa/intermediate/_category_.json

@@ -0,0 +1,8 @@
+{
+    "label": "Intermediate",
+    "position": 2,
+    "link": {
+      "type": "generated-index",
+      "description": "Learn the intermediate of the Data Structures."
+    }
+  }