The Privacy settings for Arnold McLellan prohibit the display of a Wikid Shareable Family Tree.
Shareable Trees are for sharing on Facebook, Twitter, Google+, e-mail, etc. Arnold McLellan's family tree is private. To view it, you need to be logged-in to WikiTree and on the Trusted List.
If you are the Profile Manager, you can change the Privacy Level for Arnold McLellan here. Select a level of "Private with Public Biography and Family Tree" or higher to enable their tree to be publicly shared. (Private people in the tree will still be protected.)