How to put the parent node higher than the children nodes in a drawing for a graph?

You can use

1. Graph with the option GraphLayout -> "LayeredDigraphEmbedding", or
2. LayeredGraphPlot, or
3. TreePlot specifying the root vertex in the third argument.

 Graph[{7 -> 2, 2 -> 3, 3 -> 4, 3 -> 5}, 
   VertexLabels -> "Name", 
   GraphLayout->"LayeredDigraphEmbedding"]

LayeredGraphPlot[{7 -> 2, 2 -> 3, 3 -> 4, 3 -> 5}, 
   VertexLabels -> "Name"]

same picture

TreePlot[{7 -> 2, 2 -> 3, 3 -> 4, 3 -> 5}, Automatic, 7, 
 VertexLabels-> "Name", DirectedEdges -> True]

Note: LayeredGraphPlot and TreePlot produce Graphics objects.

Graph[{7 -> 2, 2 -> 3, 3 -> 4, 3 -> 5}, VertexLabels -> "Name", 
 GraphLayout -> {"LayeredEmbedding", "RootVertex" -> 7}]