You will have to create a custom module map
file containing the header of libxml/tree.h
like so :
module libxml [system] {
header "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/libxml2/libxml/tree.h"
export *
}
Then you place this file (module.modulemap) inside a folder -module for example- and add it to your project's and target's build settings
.
You can now use @import libxml;
in your code.