Query related to SVM

Following Matlab notation: I have input data matrix X of order nx1 And a matrix Y also of order nx1 which has element value -1 or +1 with the help of regression tree i am trying to predict n+1th value of matrix X

i used the command 'tree = RegressionTree.fit(X,Y)' the tree constructed has one node and two leafs

now iam using predict command to find out the n+1th value, the n+1th test value and the predicted value has very high error.

Can anyone tell me where iam going wrong and the correct procedure to go ahead.