The first thing to consider is whether you want to design/improve data mining techniques, apply data mining techniques or do both.
The University of Minnesota is home to a wide range of data mining activities of interest to Data Science students.
The departments associated with the MS Degree in Data Science, namely the Department of Computer Science and Engineering, Department of Electrical and Computer Engineering, School of Statistics, and the School of Public Health, together house a uniquely large variety of faculty and research in data mining and data management.
I would like to work on a similar subject using "Decision Tree Technique".
Please suggest some topics or project that would make for a good masters thesis subject. Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise.