diff --git a/README.md b/README.md
index 1aee0d5..c9cce54 100644
--- a/README.md
+++ b/README.md
@@ -126,36 +126,37 @@ The "classic" Satoshi-blockchain is like a git repo with a single master branch
 <!--    
 ### Encryption knowledge
    -->
-**Encryption knowledge**    
-*   [Introduction](./Basic/crypto.md)
-*   Encryption in blockchain
+-   **Encryption knowledge**    
+    *   [Introduction](./Basic/crypto.md)
+    *   Merkle tree in blockchain
+    *   [Merkle dag ](http://www.sohu.com/a/247540268_100222281)
 <!--   
 ### Consensus
    -->
-**Consensus**  
+-   **Consensus**  
 <!--    
 ### Account and transaction model
    -->
-**Account and transaction model**  
+-   **Account and transaction model**  
 <!-- 
 ### Exchange
     -->
-**Exchange**  
+-   **Exchange**  
 <!-- 
 ### Applications
     -->
-**Applications**  
--   [Do You Need a Blockchain?](https://spectrum.ieee.org/computing/networks/do-you-need-a-blockchain)   
--   [What can't blockchain do?](https://www.jianshu.com/p/70f6a29a6296)   
--   [More](./Extension/application.md) 
+-   **Applications**  
+    -   [Do You Need a Blockchain?](https://spectrum.ieee.org/computing/networks/do-you-need-a-blockchain)   
+    -   [What can't blockchain do?](https://www.jianshu.com/p/70f6a29a6296)   
+    -   [More](./Extension/application.md) 
 <!--     
 ### Capacity expansion and chain governance
     -->
-**[Capacity expansion and chain governance](https://github.com/yfeng125/blockchain-tutorial/blob/master/doc/%E2%80%8B25.%E6%AF%94%E7%89%B9%E5%B8%81%EF%BC%9A%E6%89%A9%E5%AE%B9%E4%B9%8B%E4%BA%89%E3%80%81IFO%E4%B8%8E%E9%93%BE%E4%B8%8A%E6%B2%BB%E7%90%86.md)**   
+-   **[Capacity expansion and chain governance](https://github.com/yfeng125/blockchain-tutorial/blob/master/doc/%E2%80%8B25.%E6%AF%94%E7%89%B9%E5%B8%81%EF%BC%9A%E6%89%A9%E5%AE%B9%E4%B9%8B%E4%BA%89%E3%80%81IFO%E4%B8%8E%E9%93%BE%E4%B8%8A%E6%B2%BB%E7%90%86.md)**   
 <!--     
 ### Digital currency ranking
     -->
-**[Digital currency ranking](https://coinmarketcap.com/)**   
+-   **[Digital currency ranking](https://coinmarketcap.com/)**   
 
 <!-- -   [ ] [Consensus](<>)  
 -   [Account and transaction model](./Basic/account.md)