Always show the expand button in a tree?

I have a complex client / server system to manage master data in the industry. Much of this data is represented by a deep tree structure.

What is the best thing to do at this point?

• Always show the expand button for each node?
• Calculate in the server if the respective node has child elements and set for this a property which the client can evaluate to display the expand button?

For the latter I would then always have to query the table with the children, if there is at least one, which has the node as parent element and for each node.

The more nodes I query, the longer the query takes so synonymous. Ok, I have paging with it, but even then it is so that I have to make 101 queries for 100 elements.

I do not want the button is always displayed, but if the response time is too big, I will have no other possibility, right?