This article would cover steps to create a Visualforce Page which outputs a tree like structure wherein you could view Accounts, the Contacts related to the account and the Cases related to the Contact - All in one single tree structure.

Watch a DEMO here.....

Screenshot:
Step 1:

Download the Jquery Plugin from here. Upload this Zip file into Static Resources with the name "Jtreeview"

Step 2:

Create the Apex Class "treenodes" and paste the below code.

public class treenodes {

/* Wrapper class to contain the nodes and their children */
public class cNodes
{

 public List<Contact> parent {get; set;}
 Public Account gparent {get;set;}

 public cNodes(Account  gp, List<Contact> p)
 {
     parent = p;
     gparent = gp;
 }
}
/* end of Wrapper class */ 

Public List<cNodes> hierarchy;

Public List<cNodes> getmainnodes()
{
    hierarchy = new List<cNodes>();
    List<Account> tempparent = [Select Id,Name from Account];
    for (Integer i =0; i< tempparent.size() ; i++)
    {
        List<Contact> tempchildren = [Select Id,FirstName,LastName,(Select Id,CaseNumber,Subject from Cases) from Contact where AccountId = :tempparent[i].Id];
        hierarchy.add(new cNodes(tempparent[i],tempchildren));
     }   
    return hierarchy;
}   
}

Step 3:

Create a Visualforce Page "TreeViewDemo" and paste the below code.

<apex:page sidebar="false" controller="treenodes" showheader="false">
<!-- Include the Jquery Script files -->
    <link rel="stylesheet" href="{!URLFOR($Resource.Jtreeview,'Jquerytreeview/jquery.treeview.css')}"/>
    <script src="{!URLFOR($Resource.Jtreeview,'Jquerytreeview/jquery.js')}" type="text/javascript"></script>
    <script src="{!URLFOR($Resource.Jtreeview,'Jquerytreeview/jquery.cookie.js')}" type="text/javascript"></script>
    <script src="{!URLFOR($Resource.Jtreeview,'Jquerytreeview/jquery.treeview.js')}" type="text/javascript"></script>
<!-- End of Javascript files -->
<script type="text/javascript">
        $(function() {
            $("#tree").treeview({
                collapsed: false,
                animated: "medium",
                control:"#sidetreecontrol",
                persist: "location"
            });
        })
</script>
<br/> <br/> <br/>
<!-- Tree -->
<div class="treeheader" style="height:0px;">&nbsp;</div>
<div id="sidetreecontrol"><a href="?#"><font style="color:blue;">Collapse All</font></a> | <a href="?#"><font style="color:blue;">Expand All</font></a></div>
<ul id="tree">
    <apex:repeat value="{!mainnodes}" var="parent">
        <li><strong><apex:outputtext style="color:blue;" escape="false" value="{!parent.gparent.Name}"/></strong>
             <ul>
                 <apex:repeat value="{!parent.parent}" var="child">
                    <li><span class="formattextcon"><apex:outputtext style="color:green;" escape="false" value="{!child.LastName}"/></span>
                        <ul>
                            <apex:repeat value="{!child.Cases}" var="gchildren">
                               <li> <span class="formattextcon"> <apex:outputtext escape="false" style="color:red;" value="{!gchildren.CaseNumber}"/> <b>||</b> &nbsp;<apex:outputtext escape="false" value="{!gchildren.Subject}"/> </span> </li>
                            </apex:repeat>
                        </ul>       
                    </li>
                 </apex:repeat>  
             </ul>  
        </li>
    </apex:repeat>
</ul>
<!-- End of Tree -->       
</apex:page>

Note: You may modify the hierarchy by replacing the Objects and the queries with your required ones. Also, you may have to optimize the apex class to handle more than 100 queries as this demo has a SOQL query within a FOR loop (An Example of bad programming practice).