In this paper, we present a method to automatically extract the vessel segments and construct the vascular tree with anatomical realism from a color retinal image. The significance of the work is to assist in clinical studies of diagnosis of cardio-vascular diseases, such as hypertension, which manifest abnormalities in either venous and/or arterial vascular systems. To maximize the completeness of vessel extraction, we introduce vessel connectiveness measure to improve on an existing algorithm which applies multiscale matched filtering and vessel likelihood measure. Vessel segments are grouped using extended Kalman filter to take into consideration continuities in curvature, width, and color changes at the bifurcation or crossover point. The algorithm is tested on five images from the DRIVE database, a mixture of normal and pathological images, and the results are compared with the groundtruth images provided by a physician. The preliminary results show that our method reaches an ave...