This experiment research entitled “The Effectiveness of Tree Diagram aimed to
improve Students Vocabulary”. It was conducted at the seventh grade of SMP Negeri 2
Pekuncen in academic year 2017/2018. Each group consisted of 32 students. In collecting the
data the writer used pre-test and post-test. The mean score of experimental group before
treatment is 5.85 with the highest score of 7.5 and lowest score of 4. It means the students
vocabulary was still low. Meanwhile after the students got the treatment by using tree
diagram they got the mean score of 7.94 with the highest score 10 and the lowest score of
7.25. After analyzing the data, the writer found the t-value for experimental group is 185.545
with degree of freedom (df) 32(N-k=32-1=31). The t-table for standard significant with (df)
31 is 2.040. It can be seen that t-value is higher than t-table (185.545< 2.040). Meanwhile, the
t-value for control group shows 2017 with degree freedom (df) 31 (N-k=32-1=31). The ttable
for standard significant with (df) 31 is 2040. This shows that the t-value is lower than ttable
(2.017-2.040). It means that the hypothesis which stated that tree diagram was effective
to improve students vocabulary at the seventh grade students of SMP Negeri 2 Pekuncen in
academic year 2017/2018 was accepted.