Root Node of AST

[Rajesh Babu]

Hi,
	I want the root node of the AST built by gcc, so that I can do the 
manipulations I want to do on the intermediate nodes of AST.  Can someone 
tell me where I can find the root node of AST and the place where the 
construction of AST finishes in GCC source.

Thanks in Advance
Rajesh Babu