After you establish the root domain, you can add a new tree to the existing forest if your network plan requires multiple trees.

To create a new tree in an existing forest, run Dcpromo.exe to start the Active Directory Installation wizard. Complete the wizard by using the information in the following table.

On this wizard page Do this
Domain Controller Type Click Domain controller for a new domain.
Create Tree or Child Domain Click Create a new domain tree.
Create or Join Forest Click Place this new domain tree in an existing forest.
Network Credentials Specify the user name, password, and domain name of a user account in the Enterprise Admins group, which exists in the root domain of the forest.
New Domain Tree Specify the DNS name for the new tree.
Domain NetBIOS Name Specify the NetBIOS name for the new domain.
Database and Log Locations Specify locations for the Active Directory database and log files.
Shared System Volume Specify the location for the shared system volume.
Windows NT 4.0 RAS Servers Specify whether to weaken permissions to support users who access the network through remote access servers running Windows NT 4.0.

After you finish specifying the installation information, the Active Directory Installation wizard installs Active Directory, converts the computer to a domain controller, and adds the Active Directory consoles to the Administrative Tools menu on that computer.