I need a pattern for constructing trees of objects -

i've got code (c#) builds tree of polymorphic objects. depending on type, object may have 0-7 children. right now, objects' constructors nothing, , construct whole object tree using recursive helper function:

// pseudocode void buildtree(node root) {     if(root a) {         root.a_data = ...         root.a_child = generatenewnode(some_constraints);          buildtree(root.a_child)     } else if(root b) {         // same stuff, b.  note b may have different chldren, etc     } } 

this seems inelegant, i'm looking pattern can me here. buildtree function seems policy of kind, , i'd able use different policies in future.

oh, complicating factor. there things in buildtree conditional on earlier things buildtree has done. example, if i've ever generated b, need xyz c nodes. or if i'm generating children of a, don't generate d.

sounds need stick polymorphic method on each node, every node becomes capable of building itself.

public class node {     public virtual buildnode(ibuildstrategy strategy)     {     } } 

that way can call

root.buildnode(new initialnodebuildingstrategy()); 

to populate tree while still allowing custom strategies within subtrees.