This is what I did:
1. clone/download the branch from github to my local machine.
2. go in to the directory and do "npm install" first, then do "npm run build" for sandcastle demos or "npm run minifyRelease " for HelloWorld
Here is the install instruction page:
when i use the command "npm install cesium" in my web project ,hao can i get the 3d-tiles branch?
Since the 3d-tiles branch isn’t merged into master yet it won’t be available on npm. However 3d-tiles will be merged into master for the July release and this will no longer be an issue.
While Sean is correct about it being in the next release, you can use master (which now includes 3d-tiles) via npm via our travis build. Just change the version in package.json to http://cesium-dev.s3-website-us-east-1.amazonaws.com/cesium/master/cesium-1.34.0-master22220.tgz (these builds are only around for 90 days, so you shouldn’t use them in production).