title: How can I plot a tree (and squirrels) in R?
body: <p>Here is my tree:</p>
  
  <pre><code>tree = data.frame(branchID = c(1,11,12,111,112,1121,1122), length = c(32, 21, 19, 5, 12, 6, 2))
  
  &gt; tree
    branchID length
  1        1     32
  2       11     21
  3       12     19
  4      111      5
  5      112     12
  6     1121      6
  7     1122      2
  </code></pre>
  
  <p>This tree is in 2D and is made of branches. Each branch has an ID. <code>1</code> is the trunk. Then the trunk bifurcate into two branches, <code>11</code> on the left and <code>12</code> on the right. <code>11</code> bifurcates as well in the branches called <code>111</code> (going toward the left) and <code>112</code> (going toward the right). etc.. Each branch has a certain length.</p>
  
  <p>On this tree there are squirrels:</p>
  
  <pre><code>squirrels = data.frame(branchID = c(1,11,1121,11,111), PositionOnBranch = c(23, 12, 4, 2, 1), name=c("FluffyTail", "Ginger", "NutCracker", "SuperSquirrel", "ChipnDale"))
  
  &gt; squirrels
    branchID PositionOnBranch          name
  1        1               23    FluffyTail
  2       11               12        Ginger
  3     1121                4    NutCracker
  4       11                2 SuperSquirrel
  5      111                1     ChipnDale
  </code></pre>
  
  <p>Each squirrel is found on a specific branch. For example the <code>FluffyTail</code> is on the trunk at position 23 (the total length of the trunk being 32). <code>ChipnDale</code> is on the branch <code>111</code> at position 1 (the total length of the branch <code>111</code> is 5). The position is taken relatively to the lower extremity of the branch.</p>
  
  <p><strong>How can I plot my tree and my squirrels?</strong></p>