Sha,

The tree will move with thermal and pressure effects in the well.

You can visualise the mechanism as several pipes in parallel, all connected at one point, the tree, and each anchored by cementing at different levels down to the producing formation. The inner will be the smallest diameter, the longest and usually the highest temperature since it carries the well fluid. The outer, the conductor usually the lowest temperature and largest diameter. There may be 4 or 5 intermediate strings. Each is really a spring of differing stiffness, length and temperature. The net wellhead movement results from the solution to this stiffness puzzle.