function drawTree(a, b, x, y, C, color, level)
% Recursively draw a tree:  draw one branch and then at each defined
% recursion point draw another branch using recursion.
% (a,b) is location of the first point of the branch.
% x is vector of x coordinates of points in the branch.
% y is vector of y coordinates of points in the branch.
% C is symmetric connectivity matrix indicating which points connect.
% color is a vector or character indicating the color of the tree.
% level is the number of times further recursion takes place.

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