In this tutorial I will show you how to to do top to bottom approach in assembly of catia v5
Go to assembly tree from start in CATIA
And access to "product structure tool" from the toolbar section
Click on product from that tool bar and select the product icon from the tree and you will get the products as many as you wish in the tree.
Click on insert component and repeat the same process and same to insert part and you can arrange the tree in top to bottom way.
It can be used in automotive assembly etc