LayerSizeFunction

is an option for TreePlot that gives a function to specify the relative height to allow for each layer.

Details

LayerSizeFunction->f specifies that the difference of coordinates between layer n and layer should be proportional to .
The root or top vertices are taken to be at layer 1.
With the default setting DataRange->Automatic, LayerSizeFunction is taken to give the actual coordinate difference between layers.

Draw a tree with the first level of height 1, and the second of height 2:

Wolfram Language code: TreePlot[{1 -> 2, 1 -> 3, 2 -> 4, 2 -> 5, 3 -> 6, 3 -> 7}, LayerSizeFunction -> (#&)]

Plot a binary tree with random layer size:

Wolfram Language code: TreePlot[Flatten[Table[{i -> 2i + j - 1}, {j, 2}, {i, 2 ^ 7 - 1}]], Center, LayerSizeFunction -> (RandomReal[{-3, 3}]&)]

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