By definition, a Treemap or Block Chart is sorted by Value (descending).
Given your screenshot, I guess you are using a Treemap as a "Legend" maybe for another visualization. If so, then add a Measure with slighty different and incremental values to the Dimension values.
You coul also use a Table to accomplish the same result and maybe you could sort it more easily by giving each Level an integer value using an INLINE table in the script editor:
LOAD * INLINE [